opinion: GREGORY et al., JUDGES v. ASHCROFT, GOVERNOR OF MISSOURI
  No. 90-50.
  Argued March 18, 1991
  Decided June 20, 1991
  Jim J. Shoemake argued the cause for petitioners. With him on the briefs were Thomas J. Guilfoil and Bruce Dayton Livingston.
  James B. Deutsch, Deputy Attorney General of Missouri, argued the cause for respondent. With him on the brief were William L. Webster, Attorney General, and Michael L. Boicourt, Assistant Attorney General.
  Cathy Ventrell-Monsees filed a brief for the American Association of Retired Persons as amicus curiae urging reversal.
  Briefs of amici curiae urging affirmance were filed for the State of Colorado et al. by Scott Harshbarger, Attorney General of Massachusetts, H. Reed Witherby, Special Assistant Attorney General, and Thomas A. Bar-uico, Assistant Attorney General, and by the Attorneys General for their respective jurisdictions as follows: Gale A. Norton of Colorado, Robert A. Butterworth of Florida, Warren Price III of Hawaii, Hubert H. Httmphrey III of Minnesota, Donald Stenberg of Nebraska, RobeH Del Tufo of New Jersey, Nicholas J. Spaeth of North Dakota, Ernest D. Preate, Jr., of Pennsylvania, Hector Rivera-Cruz of Puerto Rico, James E. O’Neil of Rhode Island, T. Travis Medlock of South Carolina, and Joseph B. Meyer of Wyoming; for the State of Connecticut by Richard Blumenthal, Attorney General, and Arnold B. Feigin and Daniel R. Schaefer, Assistant Attorneys General; for the State of Vermont, Office of Court Administrator, by William B. Gray; for the Missouri Bar by Karen M. Iverson and Timothy K. McNamara; for the National Governors Association et al. by Richard Ruda, Michael J. Wahoske, and Mark B. Rotenberg; and for the Washington Legal Foundation by John C. Cozad, W. Dennis Cross, R. Christopher Abele, Daniel J. Popeo, and John C. Scully.
  Daniel G. Spraul filed a brief for Judge John W. Keefe as amicus curiae.
  Justice O’Connor
  delivered the opinion of the Court.
  Article V, § 26, of the Missouri Constitution provides that “[a]ll judges other than municipal judges shall retire at the age of seventy years.” We consider whether this mandatory retirement provision violates the federal Age Discrimination in Employment Act of 1967 (ADEA or Act), 81 Stat. 602, as amended, 29 U. S. C. §§ 621-634, and whether it comports with the federal constitutional prescription of equal protection of the laws.
  I
  Petitioners are Missouri state judges. Judge Ellis Gregory, Jr., is an associate circuit judge for the Twenty-first Judicial Circuit. Judge Anthony P. Nugent, Jr., is a judge of the Missouri Court of Appeals, Western District. Both are subject to the § 26 mandatory retirement provision. Petitioners were appointed to office by the Governor of Missouri, pursuant to the Missouri Non-Partisan Court Plan, Mo. Const., Art. V, §§ 25(a)-25(g). Each has, since his appointment, been retained in office by means of a retention election in which the judge ran unopposed, subject only to a “yes or no” vote. See Mo. Const., Art. V, § 25(c)(1).
  Petitioners and two other state judges filed suit against John D. Ashcroft, the Governor of Missouri, in the United States District Court for the Eastern District of Missouri, challenging the validity of the mandatory retirement provision. The judges alleged that the provision violated both the ADEA and the Equal Protection Clause of the Fourteenth Amendment to the United States Constitution. The Governor filed a motion to dismiss.
  The District Court granted the motion, holding that Missouri’s appointed judges are not protected by the ADEA because they are “appointees ... ‘on a policymaking level’ ” and therefore are excluded from the Act’s definition of “employee.” App. to Pet. for Cert. 22. The court held also that the mandatory retirement provision does not violate the Equal Protection Clause because there is a rational basis for the distinction between judges and other state officials to whom no mandatory retirement age applies. Id., at 23.
  The United States Court of Appeals for the Eighth Circuit affirmed the dismissal. 898 F. 2d 598 (1990). That court also held that appointed judges are “ ‘appointee[s] on the poli-cymaking level,’” and are therefore not covered under the ADEA. Id., at 604. The Court of Appeals held as well that Missouri had a rational basis for distinguishing judges who had reached the age of 70 from those who had not. Id., at 606.
  We granted certiorari on both the ADEA and equal protection questions, 498 U. S. 979 (1990), and now affirm.
  HH ) — l
  The ADEA makes it unlawful for an employer to discharge any individual” who is at least 40 years old “because of such individual’s age.” 29 U. S. C. §§ 623(a), 631(a). The term “employer” is defined to include “a State or political subdivision of a State.” § 630(b)(2). Petitioners work for the State of Missouri. They contend that the Missouri mandatory retirement requirement for judges violates the ADEA.
  A
  As every schoolchild learns, our Constitution establishes a system of dual sovereignty between the States and the Federal Government. This Court also has recognized this fundamental principle. In Tafflin v. Levitt, 493 U. S. 455, 458 (1990), “[w]e beg[a]n with the axiom that, under our federal system, the States possess sovereignty concurrent with that of the Federal Government, subject only to limitations imposed by the Supremacy Clause.” Over 120 years ago, the Court described the constitutional scheme of dual sovereigns:
  “‘[TJhe people of each State compose a State, having its own government, and endowed with all the functions essential to separate and independent existence,’ . . . ‘[WJithout the States in union, there could be no such political body as the United States.’ Not only, therefore, can there be no loss of separate and independent autonomy to the States, through their union under the Constitution, but it may be not unreasonably said that the preservation of the States, and the maintenance of their governments, are as much within the design and care of the Constitution as the preservation of the Union and the maintenance of the National government. The Constitution, in all its provisions, looks to an indestructible Union, composed of indestructible States.” Texas v. White, 7 Wall. 700, 725 (1869), quoting Lane County v. Oregon, 7 Wall. 71, 76 (1869).
  The Constitution created a Federal Government of limited powers. “The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.” U. S. Const., Arndt. 10. The States thus retain substantial sovereign authority under our constitutional system. As James Madison put it:
  “The powers delegated by the proposed Constitution to the federal government are few and defined. Those which are to remain in the State governments are numerous and indefinite. . . . The powers reserved to the several States will extend to all the objects which, in the ordinary course of affairs, concern the lives, liberties, and properties of the people, and the internal order, improvement, and prosperity of the State.” The Federalist No. 45, pp. 292-293 (C. Rossiter ed. 1961).
  This federalist structure of joint sovereigns preserves to the people numerous advantages. It assures a decentralized government that will be more sensitive to the diverse needs of a heterogenous society; it increases opportunity for citizen involvement in democratic processes; it allows for more innovation and experimentation in government; and it makes government more responsive by putting the States in competition for a mobile citizenry. See generally McConnell, Federalism: Evaluating the Founders’ Design, 54 U. Chi. L. Rev. 1484, 1491-1511 (1987); Merritt, The Guarantee Clause and State Autonomy: Federalism for a Third Century, 88 Colum. L. Rev. 1, 3-10 (1988).
  Perhaps the principal benefit of the federalist system is a check on abuses of government power. “The ‘constitutionally mandated balance of power’ between the States and the Federal Government was adopted by the Framers to ensure the protection of ‘our fundamental liberties.’” Atascadero State Hospital v. Scanlon, 473 U. S. 234, 242 (1985), quoting Garcia v. San Antonio Metropolitan Transit Authority, 469 U. S. 528, 572 (1985) (Powell, J., dissenting). Just as the separation and independence of the coordinate branches of the Federal Government serve to prevent the accumulation of excessive power in any one branch, a healthy balance of power between the States and the Federal Government will reduce the risk of tyranny and abuse from either front. Alexander Hamilton explained to the people of New York, perhaps optimistically, that the new federalist system would suppress completely “the attémpts of the government to establish a tyranny”:
  “[I]n a confederacy the people, without exaggeration, may be said to be entirely the masters of their own fate. Power being almost always the rival of power, the general government will at all times stand ready to check the usurpations of the state governments, and these will have the same disposition towards the general government. The people, by throwing themselves into either scale, will infallibly make it preponderate. If their rights are invaded by either, they can make use of the other as the instrument of redress.” The Federalist No. 28, pp. 180-181 (C. Rossiter ed. 1961).
  James Madison made much the same point:
  “In a single republic, all the power surrendered by the people is submitted to the administration of a single government; and the usurpations are guarded against by a division of the government into distinct and separate departments. In the compound republic of America, the power surrendered by the people is first divided between two distinct governments, and then the portion allotted to each subdivided among distinct and separate departments. Hence a double security arises to the rights of the people. The different governments will control each other, at the same time that each will be controlled by itself.” Id., No. 51, p. 323.
  One fairly can dispute whether our federalist system has been quite as successful in checking government abuse as Hamilton promised, but there is no doubt about the design. If this “double security” is to be effective, there must be a proper balance between the States and the Federal Government. These twin powers will act as mutual restraints only if both are credible. In the tension between federal and state power lies the promise of liberty.
  The Federal Government holds a decided advantage in this delicate balance: the Supremacy Clause. U. S. Const., Art. VI, cl. 2. As long as it is acting within the powers granted it | under the Constitution, Congress may impose its will on the | States. Congress may legislate in areas traditionally regulated by the States. This is an extraordinary power in a federalist system. It is a power that we must assume Congress does not exercise lightly.
  The present case concerns a state constitutional provision through which the people of Missouri establish a qualification for those who sit as their judges. This provision goes beyond an area traditionally regulated by the States; it is a decision of the most fundamental sort for a sovereign entity. . Through the structure of its government, and the character of those who exercise government authority, a State defines itself as a sovereign. “It is obviously essential to the independence of the States, and to their peace and tranquility, that their power to prescribe the qualifications of their own officers . . . should be exclusive, and free from external interference, except so far as plainly provided by the Constitution of the United States.” Taylor v. Beckham, 178 U. S. 548, 570-571 (1900). See also Boyd v. Nebraska ex rel. Thayer, 143 U. S. 135, 161 (1892) (“Each State has the power to prescribe the qualifications of its officers and the manner in which they shall be chosen”).
  Congressional interference with this decision of the people of Missouri, defining their constitutional officers, would upset the usual constitutional balance of federal and state powers. For this reason, “it is incumbent upon the federal courts to be certain of Congress’ intent before finding that federal law overrides” this balance. Atascadero, supra, at 243. We explained recently:
  “[I]f Congress intends to alter the ‘usual constitutional balance between the States and the Federal Government,’ it must make its intention to do so ‘unmistakably clear in the language of the statute.’ Atascadero State Hospital v. Scanlon, 473 U. S. 234, 242 (1985); see also Pennhurst State School and Hospital v. Halderman, 465 U. S. 89, 99 (1984). Atascadero was an Eleventh Amendment case, but a similar approach is applied in other contexts. Congress should make its intention ‘clear and manifest’ if it intends to pre-empt the historic powers of the States, Rice v. Santa Fe Elevator Corp., 331 U. S. 218, 230 (1947) .... ‘In traditionally sensitive areas, such as legislation affecting the federal balance, the requirement of clear statement assures that the legislature has in fact faced, and intended to bring into issue, the critical matters involved in the judicial decision.’ United States v. Bass, 404 U. S. 336, 349 (1971).” Will v. Michigan Dept. of State Police, 491 U. S. 58, 65 (1989).
  This plain statement rule is nothing more than an acknowledgment that the States retain substantial sovereign powers under our constitutional scheme, powers with which Congress does not readily interfere.
  In a recent line of authority, we have acknowledged the unique nature of state decisions that “go to the heart of representative government.” Sugarman v. Dougall, 413 U. S. 634, 647 (1973). Sugarman was the first in a series of cases to consider the restrictions imposed by the Equal Protection Clause of the Fourteenth Amendment on the ability of state and local governments to prohibit aliens from public employment. In that case, the Court struck down under the Equal Protection Clause a New York City law that provided a flat ban against the employment of aliens in a wide variety of city jobs. Ibid.
  The Court did not hold, however, that alienage could never justify exclusion from public employment. We recognized explicitly the States’ constitutional power to establish the qualifications for those who would govern:
  “Just as ‘the Framers of the Constitution intended the States to keep for themselves, as provided in the Tenth Amendment, the power to regulate elections,’ Oregon v. Mitchell, 400 U. S. 112, 124-125 (1970) (footnote omitted) (opinion of Black, J.); see id., at 201 (opinion of Harlan, J.), and id., at 293-294 (opinion of Stewart, J.), “[e]ach State has the power to prescribe the qualifications of its officers and the manner in which they shall be chosen.” Boyd v. Thayer, 143 U. S. 135, 161 (1892). See Luther v. Borden, 7 How. 1, 41 (1849); Pope v. Williams, 193 U. S. 621, 632-633 (1904). Such power inheres in the State by virtue of its obligation, already noted above, ‘to preserve the basic conception of a political community.’ Dunn v. Blumstein, 405 U. S. [330, 344 (1972)]. And this power and responsibility of the State applies, not only to the qualifications of voters, but also to persons holding state elective and important non-elective executive, legislative, and judicial positions, for officers who participate directly in the formulation, execution, or review of broad public policy perform functions that go to the heart of representative government.” Ibid.
  We explained that, while the Equal Protection Clause provides a check on such state authority, “our scrutiny will not be so demanding where we deal with matters resting firmly within a State’s constitutional prerogatives.” Id., at 648. This rule “is no more than ... a recognition of a State’s constitutional responsibility for the establishment and operation of its own government, as well as the qualifications of an appropriately designated class of public office holders. U. S. Const. Art. IV, § 4; U. S. Const. Amdt. X; Luther v. Borden, supra; see In re Duncan, 139 U. S. 449, 461 (1891).” Ibid.
  In several subsequent cases we have applied the “political function” exception to laws through which States exclude aliens from positions “intimately related to the process of democratic self-government.” See Bernal v. Fainter, 467 U. S. 216, 220 (1984). See also Nyquist v. Mauclet, 432 U. S. 1, 11 (1977); Foley v. Connelie, 435 U. S. 291, 295-296 (1978); Ambach v. Norwick, 441 U. S. 68, 73-74 (1979); Cabell v. Chavez-Salido, 454 U. S. 432, 439-441 (1982). “We have . . . lowered our standard of review when evaluating the validity- of exclusions that entrust only to citizens important elective and nonelective positions whose operations ‘go to the heart of representative government.’” Bernal, 467 U. S., at 221 (citations omitted).
  These cases stand in recognition of the authority of the people of the States to determine the qualifications of their most important government officials. It is an authority that lies at “‘the heart of representative government.’” Ibid. It is a power reserved to the States under the Tenth Amendment and guaranteed them by that provision of the Constitution under which the United States “guarantee^] to every State in this Union a Republican Form of Government.” U. S. Const., Art. IV, § 4. See Sugarman, supra, at 648 (citing the Guarantee Clause and the Tenth Amendment). See also Merritt, 88 Colum. L. Rev., at 50-55.
  The authority of the people of the States to determine the qualifications of their government officials is, of course, not without limit. Other constitutional provisions, most notably the Fourteenth Amendment, proscribe certain qualifications; our review of citizenship requirements under the political function exception is less exacting, but it is not absent. Here, we must decide what Congress did in extending the ADEA to the States, pursuant to its powers under the Commerce Clause. See EEOC v. Wyoming, 460 U. S. 226 (1983) (the extension of the ADEA to employment by state and local governments was a valid exercise of Congress’ powers under the Commerce Clause). As against Congress’ powers “[t]o regulate Commerce . . . among the several States,” U. S. Const., Art. I, § 8, cl. 3, the authority of the people of the States to determine the qualifications of their government officials may be inviolate.
  We are constrained in our ability to consider the limits that the state-federal balance places on Congress’ powers under the Commerce Clause. See Garcia v. San Antonio Metropolitan Transit Authority, 469 U. S. 528 (1985) (declining to review limitations placed on Congress’ Commerce Clause powers by our federal system). But there is no need to do so if we hold that the ADEA does not apply to state judges. Application of the plain statement rule thus may avoid a potential constitutional problem. Indeed, inasmuch as this Court in Garcia has left primarily to the political process the protection of the States against intrusive exercises of Congress’ Commerce Clause powers, we must be absolutely certain that Congress intended such an exercise. “[T]o give the state-displacing weight of federal law to mere congressional ambiguity would evade the very procedure for lawmaking on which Garcia relied to protect states’ interests.” L. Tribe, American Constitutional Law §6-25, p. 480 (2d ed. 1988).
  B
  In 1974, Congress extended the substantive provisions of the ADEA to include the States as employers. Pub. L. 93-259, § 28(a), 88 Stat. 74, 29 U. S. C. § 630(b)(2). At the same time, Congress amended the definition of “employee” to exclude all elected and most high-ranking government officials. Under the Act, as amended:
  “The term ‘employee’ means an individual employed by any employer except that the term ‘employee’ shall not include any person elected to public office in any State or political subdivision of any State by the qualified voters thereof, or any person chosen by such officer to be on such officer’s personal staff, or an appointee on the policymaking level or an immediate adviser with respect to the exercise of the constitutional or legal powers of the office.” 29 U. S. C. § 630(f).
  Governor Ashcroft contends that the § 630(f) exclusion of certain public officials also excludes judges, like petitioners, who are appointed to office by the Governor and are then subject to retention election. The Governor points to two passages in § 630(f). First, he argues, these judges are selected by an elected official and, because they make policy, are “appointee[s] on the policymaking level.”
  Petitioners counter that judges merely resolve factual disputes and decide questions of law; they do not make policy. Moreover, petitioners point out that the policymaking-level exception is part of a trilogy, tied closely to the elected-official exception. Thus, the Act excepts elected officials and: (1) “any person chosen by such officer to be on such officer’s personal staff”; (2) “an appointee on the policymaking level”; and (3) “an immediate advisor with respect to the exercise of the constitutional or legal powers of the office.” Applying the maxim of statutory construction noscitur a sock's — that a word is known by the company it keeps — petitioners argue that since (1) and (3) refer only to those in close working relationships with elected officials, so too must (2). Even if it can be said that judges may make policy, petitioners contend, they do not do so at the behest of an elected official.
  Governor Ashcroft relies on the plain language of the statute: It exempts persons appointed “at the policymaking level.” The Governor argues that state judges, in fashioning and applying the common law, make policy. Missouri is a common law state. See Mo. Rev. Stat. § 1.010 (1986) (adopting “[t]he common law of England” consistent with federal and state law). The common law, unlike a constitution or statute, provides no definitive text; it is to be derived from the interstices of prior opinions and a well-considered judgment of what is best for the community. As Justice Holmes put it:
  “The very considerations which judges most rarely mention, and always with an apology, are the secret root from which the law draws all the juices of life. I mean, of course, considerations of what is expedient for the community concerned. Every important principle which is developed by litigation is in fact and at bottom the result of more or less definitely understood views of public policy; most generally, to be sure, under our practice and traditions, the unconscious result of instinctive preferences and inarticulate convictions, but nonetheless traceable to views of public policy in the last analysis.” 0. Holmes, The Common Law 35-36 (1881).
  Governor Ashcroft contends that Missouri judges make policy in other ways as well. The Missouri Supreme Court and Courts of Appeals have supervisory authority over inferior courts. Mo. Const., Art. V, § 4. The Missouri Supreme Court has the constitutional duty to establish rules of practice and procedure for the Missouri court system, and inferior courts exercise policy judgment in establishing local rules of practice. See Mo. Const., Art. V, § 5. The state courts have supervisory powers over the state'-bar, with the Missouri Supreme Court given the authority to develop disciplinary rules. See Mo. Rev. Stat. §§ 484.040, 484.200-484.270 (1986); Rules Governing the Missouri Bar and the Judiciary (1991).
  The Governor stresses judges’ policymaking responsibilities, but it is far from plain that the statutory exception requires that judges actually make policy. The statute refers to appointees “on the policymaking level,” not to appointees “who make policy.” It may be sufficient that the appointee is in a position requiring the exercise of discretion concerning issues of public importance. This certainly describes the bench, regardless of whether judges might be considered policymakers in the same sense as the executive or legislature.
  Nonetheless, “appointee at the policymaking level,” particularly in the context of the other exceptions that surround it, is an odd way for Congress to exclude judges; a plain statement that judges are not “employees” would seem the most efficient phrasing. But in this case we are not looking for a plain statement that judges are excluded. We will not read the ADEA to cover state judges unless Congress has made it clear that judges are included. This does not mean that the Act must mention judges explicitly, though it does not. Cf. Dellmuth v. Muth, 491 U. S. 223, 233 (1989) (Sca-lia, J., concurring). Rather, it must be plain to anyone reading the Act that it covers judges. In the context of a statute that plainly excludes most important state public officials, “appointee on the policymaking level” is sufficiently broad that we cannot conclude that the statute plainly covers appointed state judges. Therefore, it does not.
  The ADEA plainly covers all state employees except those excluded by one of the exceptions. Where it is unambiguous that an employee does not fall within one of the exceptions, the Act states plainly and unequivocally that the employee is included. It is at least ambiguous whether a state judge is an “appointee on the policymaking level.”
  Governor Ashcroft points also to the “person elected to public office” exception. He contends that because petitioners — although appointed to office initially — are subject to retention election, they are “elected to public office” under the ADEA. Because we conclude that petitioners fall presumptively under the policymaking-level exception, we need not answer this question.
  C
  The extension of the ADEA to employment by state and local governments was a valid exercise of Congress’ powers under the Commerce Clause. EEOC v. Wyoming, 460 U. S. 226 (1983). In Wyoming, we reserved the questions whether Congress might also have passed the ADEA extension pursuant to its powers under § 5 of the Fourteenth Amendment, and whether the extension would have been a valid exercise of that power. Id., at 243, and n. 18. We noted, however, that the principles of federalism that constrain Congress’ exercise of its Commerce Clause powers are attenuated when Congress acts pursuant to its powers to enforce the Civil War Amendments. Id., at 243, and n. 18, citing City of Rome v. United States, 446 U. S. 156, 179 (1980). This is because those “Amendments were specifically designed as an expansion of federal power and an intrusion on state sovereignty.” Id., at 179. One might argue, therefore, that if Congress passed the ADEA extension under its §5 powers, the concerns about federal intrusion into state government that compel the result in this case might carry less weight.
  By its terms, the Fourteenth Amendment contemplates terference with state authority: “No State shall. . . deny to any person within its jurisdiction the equal protection of the laws.” U. S. Const., Arndt. 14. But this Court has never held that the Amendment may be applied in complete disregard for a State’s constitutional powers. Rather, the Court has recognized that the States’ power to define the qualifications of their officeholders has force even as against the proscriptions of the Fourteenth Amendment.
  We return to the political-function cases. In Sugarman, the Court noted that “aliens as a class ‘are a prime example of a “discrete and insular” minority (see United States v. Carolene Products Co., 304 U. S. 144, 152-153, n. 4 (1938)),’ and that classifications based on alienage are ‘subject to close judicial scrutiny.’” 413 U. S., at 642, quoting Graham v. Richardson, 403 U. S. 365, 372 (1971). The Sugarman Court held that New York City had insufficient interest in preventing aliens from holding a broad category of public jobs to justify the blanket prohibition. 413 U. S., at 647. At the same time, the Court established the rule that scrutiny under the Equal Protection Clause “will not be so demanding where we deal with matters resting firmly within a State’s constitutional prerogatives.” Id., at 648. Later cases have reaffirmed this practice. See Foley v. Connelie, 435 U. S. 291 (1978); Ambach v. Norwick, 441 U. S. 68 (1979); Cabell v. Chavez-Salido, 454 U. S. 432 (1982). These cases demonstrate that the Fourteenth Amendment does not override all principles of federalism.
  Of particular relevance here is Pennhurst State School and Hospital v. Halderman, 451 U. S. 1 (1981). The question in that case was whether Congress, in passing a section of the Developmentally Disabled Assistance and Bill of Rights Act, 42 U. S. C. § 6010 (1982 ed.), intended to place an obligation on the States to provide certain kinds of treatment to the disabled. Respondent Halderman argued that Congress passed § 6010 pursuant to § 5 of the Fourteenth Amendment, and therefore that it was mandatory on the States, regardless of whether they received federal funds. Petitioner and the United States, as respondent, argued that, in passing § 6010, Congress acted pursuant to its spending power alone. Consequently, § 6010 applied only to States accepting federal funds under the Act.
  The Court was required to consider the “appropriate test for determining when Congress intends to enforce” the guarantees of the Fourteenth Amendment. 451 U. S., at 16. We adopted a rule fully cognizant of the traditional power of the States: “Because such legislation imposes congressional policy on a State involuntarily, and because it often intrudes on traditional state authority, we should not quickly attribute to Congress an unstated intent to act under its authority to enforce the Fourteenth Amendment.” Ibid. Because Congress nowhere stated its intent to impose mandatory obligations on the States under its § 5 powers, we concluded that Congress did not do so. Ibid.
  The Pennhurst rule looks much like the plain statement rule we apply today. In EEOC v. Wyoming, the Court explained that Pennhurst established a rule of statutory construction to be applied where statutory intent is ambiguous. 460 U. S., at 244, n. 18. In light of the ADE A’s clear exclusion of most important public officials, it is at least ambiguous whether Congress intended that appointed judges nonetheless be included. In the face of such ambiguity, we will not attribute to Congress an intent to intrude on state governmental functions regardless of whether Congress acted pursuant to its Commerce Clause powers or § 5 of the Fourteenth Amendment.
  Ill
  Petitioners argue that, even if they are not covered by the ADEA, the Missouri Constitution’s mandatory retirement provision for judges violates the Equal Protection Clause of the Fourteenth Amendment to the United States Constitution. Petitioners contend that there is no rational basis for the decision of the people of Missouri to preclude those aged 70 and over from serving as their judges. They claim that the mandatory retirement provision makes two irrational distinctions: between judges who have reached age 70 and younger judges, and between judges 70 and over and other state employees of the same age who are not subject to mandatory retirement.
  Petitioners are correct to assert their challenge at the level of rational basis. This Court has said repeatedly that age is not a suspect classification under the Equal Protection Clause. See Massachusetts Bd. of Retirement v. Murgia, 427 U. S. 307, 313-314 (1976); Vance v. Bradley, 440 U. S. 93, 97 (1979); Cleburne v. Cleburne Living Center, Inc., 473 U. S. 432, 441 (1986). Nor do petitioners claim that they have a fundamental interest in serving as judges. The State need therefore assert only a rational basis for its age classification. See Murgia, supra, at 314; Bradley, 440 U. S., at 97. In cases where a classification burdens neither a suspect group nor a fundamental interest, “courts are quite reluctant to overturn governmental action on the ground that it denies equal protection of the laws.” Ibid. In this case, we are dealing not merely with government action, but with a state constitutional provision approved by the people of Missouri as a whole. This constitutional provision reflects both the considered judgment of the state legislature that proposed it and that of the citizens of Missouri who voted for it. See 1976 Mo. Laws 812 (proposing the mandatory retirement provision of § 26); Mo. Const., Art. XII, §§ 2(a), 2(b) (describing the amendment process). “[W]e will not overturn such a [law] unless the varying treatment of different groups or persons is so unrelated to the achievement of any combination of legitimate purposes that we can only conclude that the [people’s] actions were irrational.” Bradley, supra, at 97. See also Pennell v. San Jose, 486 U. S. 1, 14 (1988).
  Governor Ashcroft cites O’Neil v. Baine, 568 S. W. 2d 761 (Mo. 1978) (en banc), as a fruitful source of rational bases. In O’Neil, the Missouri Supreme Court — to whom Missouri Constitution Article V, § 26, applies — considered an equal protection challenge to a state statute that established a mandatory retirement age of 70 for state magistrate and probate judges. The court upheld the statute, declaring numerous legitimate state objectives it served: “The statute draws a line at a certain age which attempts to uphold the high competency for judicial posts and which fulfills a societal demand for the highest caliber of judges in the system”; “the statute . . . draws a legitimate line to avoid the tedious and often perplexing decisions to determine which judges after a certain age are physically and mentally qualified and those who are not”; “mandatory retirement increases the opportunity for qualified persons ... to share in the judiciary and permits an orderly attrition through retirement”; “such a mandatory provision also assures predictability and ease in establishing and administering judges’ pension plans.” Id., at 766-767. Any one of these explanations is sufficient to rebut the claim that “the varying treatment of different groups or persons [in § 26] is so unrelated to the achievement of any combination of legitimate purposes that we can only conclude that the [people’s] actions were irrational.” Bradley, supra, at 97.
  The people of Missouri have a legitimate, indeed compelling, interest in maintaining a judiciary fully capable of performing the demanding tasks that judges must perform. It is an unfortunate fact of life that physical and mental capacity sometimes diminish with age. See Bradley, supra, at 111—112; Murgia, supra, at 315. The people may therefore wish to replace some older judges. Voluntary retirement will not always be sufficient. Nor may impeachment — with its public humiliation and elaborate procedural machinery — serve acceptably the goal of a fully functioning judiciary. See Mo. Const., Art. VII, §§ 1-3.
  The election process may also be inadequate. Whereas the electorate would be expected to discover if their governor or state legislator were not performing adequately and vote the official out of office, the same may not be true of judges. Most voters never observe state judges in action, nor read judicial opinions. State judges also serve longer terms of office than other public officials, making them — deliberately— less dependent on the will of the people. Compare Mo. Const., Art. V, § 19 (Supreme Court justices and Court of Appeals judges serve 12-year terms; Circuit Court judges 6 years), with Mo. Const., Art. IV, § 17 (Governor, Lieutenant Governor, secretary of state, state treasurer, and attorney general serve 4-year terms) and Mo. Const., Art. III, § 11 (state representatives serve 2-year terms; state senators 4 years). Most of these judges do not run in ordinary elections. See Mo. Const., Art. V, § 25(a). The people of Missouri rationally could conclude that retention elections — in which state judges run unopposed at relatively long intervals — do not serve as an adequate check on judges whose performance is deficient. Mandatory retirement is a reasonable response to this dilemma.
  This is also a rational explanation for the fact that state judges are subject to a mandatory retirement provision, while other state officials — whose performance is subject to greater public scrutiny, and who are subject to more standard elections — are not. Judges’ general lack of accountability explains also the distinction between judges and other state employees, in whom a deterioration in performance is more readily discernible and who are more easily removed.
  The Missouri mandatory retirement provision, like all legal classifications, is founded on a generalization. It is far from true that all judges suffer significant deterioration in performance at age 70. It is probably not true that most do. It may not be true at all. But a State “ ‘does not violate the Equal Protection Clause merely because the classifications made by its laws are imperfect.’” Murgia, 427 U. S., at 316, quoting Dandridge v. Williams, 397 U. S. 471, 485 (1970). “In an equal protection case of this type . . . those challenging the . . . judgment [of the people] must convince the court that the . . . facts on which the classification is apparently based could not reasonably be conceived to be true by the . . . decisionmaker.” Bradley, 440 U. S., at 111. The people of Missouri rationally could conclude that the threat of deterioration at age 70 is sufficiently great, and the alternatives for removal sufficiently inadequate, that they will require all judges to step aside at age 70. This classification does not violate the Equal Protection Clause.
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  The people of Missouri have established a qualification for those who would be their judges. It is their prerogative as citizens of a sovereign State to do so. Neither the ADEA nor the Equal Protection Clause prohibits the choice they have made. Accordingly, the judgment of the Court of Appeals is
  Affirmed.
  Justice White believes that the “political function” cases are inappo-site because they involve limitations on “judicially created scrutiny” rather than “Congress’ legislative authority,” which is at issue here. Post, at 477. He apparently suggests that Congress has greater authority to interfere with state sovereignty when acting pursuant to its Commerce Clause powers than this Court does when applying the Fourteenth Amendment. Elsewhere in his opinion, Justice White emphasizes that the Fourteenth Amendment was designed as an intrusion on state sovereignty. See post, at 480. That being the case, our diminished scrutiny of state laws in the “political function” cases, brought under the Fourteenth Amendment, argues strongly for special care when interpreting alleged congressional intrusions into state sovereignty under the Commerce Clause.
choices: stay, petition, or motion granted affirmed (includes modified) reversed reversed and remanded vacated and remanded affirmed and reversed (or vacated) in part affirmed and reversed (or vacated) in part and remanded vacated petition denied or appeal dismissed certification to or from a lower court no disposition