opinion: Mr. Justice Stewart
  delivered the opinion of the Court.
  A provision of the Immigration and Nationality Act requires that an alien who applies for naturalization as a United States citizen must establish that during the five years preceding the filing of his petition he has been “a person of good moral character.” Another provision specifies that no applicant may be found to be a person of good moral character who, within that period, “has given false testimony for the purpose of obtaining any benefits” under the Act. The petitioner, an alien who entered this country from Hungary in 1956, filed a petition for naturalization in the United States District Court for the District of Massachusetts in 1962. At the final hearing the Attorney General appeared by counsel in opposition to the petition. Following this hearing the District Judge denied the petition, finding that the petitioner had testified falsely to facilitate his naturalization, and therefore could not, under the law, be found to be a person of good moral character within the statutory period. The Court of Appeals affirmed, and we granted certiorari.
  During the preparation of his application to file a petition for naturalization, the petitioner was asked the following question: “Have you ever, in the United States or in any other place, (a) been a member of, or in any other way connected with, or associated with the Communist Party either directly, or indirectly through another organization, group, or person?” The petitioner, under oath, answered “No.” On two subsequent occasions during the preliminary proceedings on his petition for naturalization, the petitioner again swore that he had never been a member of the Communist Party.
  At the final hearing before the District Judge, the Government produced two witnesses whose testimony indicated that the petitioner had been a member of the Communist Party in Hungary. Dr. Pal Halasz stated that he had known the petitioner when they were both students at the University of Budapest Medical School and had seen the petitioner attend Communist Party meetings there on one or more occasions. While such meetings were sometimes open to persons who were not Party members, and Dr. Halasz was not sure that the petitioner was a Party member, his attendance at Party-meetings gave Dr. Halasz the impression that the petitioner was a member. Dr. Gyorgy Kury related that he had attended a study group at the University in September 1948. These groups met to discuss Marxist-Leninist ideology, and students were required to attend regardless of Party membership. One student in each group was responsible for leading this discussion. Dr. Kury testified that, at the meeting in question, the petitioner introduced himself as a member of the Communist Party and the student leader responsible for the group’s ideological education. Dr. Kury further testified that the petitioner had told the group that he had become a member of the Communist Party after Soviet troops had occupied Hungary in 1945.
  The petitioner testified that he had never been a Party member or the ideological leader of any student discussion group. He related the heavy pressures on students at the University to attend Party functions and become members, and admitted that these pressures had led him to attend some open Party meetings as a nonmember, but added that he had not been an active participant at these meetings. The petitioner also emphasized his religious upbringing and other factors in his personal life which, he contended, made it unlikely that he would become a Party member. The petitioner’s wife testified that he had never been a Party member, and four other witnesses stated that, while in Hungary and after his arrival in the United States, the petitioner had expressed his strong opposition to the Communist Party and the Communist regime in Hungary.
  Basing his decision solely on his own evaluation of the testimony adduced at this hearing, the District Judge concluded that the petitioner had become a Party member in 1945 and had remained a member for an indefinite number of years, that the petitioner had attended meetings of the Party, and that he had instructed student study groups in Communist ideology. Accordingly, the court concluded that the petitioner had testified falsely in the preliminary naturalization proceedings, and denied his application for citizenship on the ground that he was, therefore, “not a person of good moral character within the meaning of the Immigration and Nationality Act.”
  The petitioner asks us to reject as “clearly erroneous” the factual conclusion about his Party membership reached by the District Judge and accepted by the Court of Appeals. In order to do so, we would be forced to disregard this Court’s repeated pronouncements that it “cannot undertake to review concurrent findings of fact by two courts below in the absence of a very obvious and exceptional showing of error.” E. g., Graver Mfg. Co. v. Linde Co., 336 U. S. 271, 275. For there was no “very obvious and exceptional” error in the conclusion of the two courts below that the petitioner had been a member of the Communist Party. The testimony of Dr. Kury gave a concrete basis for this conclusion, and that of Dr. Halasz lent it further evidentiary support. The conclusion of the courts below is not inconsistent with the possibility that the petitioner may have harbored a strong opposition to the Party which he bared to his friends. For the petitioner may have merely joined the Party as a nominal member in deference to the strong pressures which the Party exerted on students to become members, pressures which several witnesses, including the petitioner himself, recited in detail.
  The policy underlying the “two-court” rule is obvious. This Court possesses no empirical expertise to set against the careful and reasonable conclusions of lower courts on purely factual issues. When, as here, resolution of the disputed factual issues turns largely on an assessment of the relative credibility of witnesses whose testimonial demeanor was observed only by the trial court, the rule has particular force. To be sure, this Court has not hesitated to undertake independent examination of factual issues when constitutional claims may depend on their resolution. See, e. g., Napue v. Illinois, 360 U. S. 264, 271-272; Fiske v. Kansas, 274 U. S. 380, 385-386. Cf. Hoffa v. United States, ante, p. 293. But this exceptional doctrine has no application to the present case, for the petitioner makes no claim that any constitutional issues are involved here.
  Different considerations do not govern merely because this is a naturalization case. When the Government seeks to strip a person of citizenship already acquired, or deport a resident alien and send him from our shores, it carries the heavy burden of proving its case by “clear, unequivocal, and convincing evidence.” But when an alien seeks to obtain the privileges and benefits of citizenship, the shoe is on the other foot. He is the moving party, affirmatively asking the Government to endow him with all the advantages of citizenship. Because that status, once granted, cannot lightly be taken away, the Government has a strong and legitimate interest in ensuring that only qualified persons are granted citizenship. For these reasons, it has been universally accepted that the burden is on the alien applicant to show his eligibility for citizenship in every respect. This Court has often stated that doubts “should be resolved in favor of the United States and against the claimant.” E. g., United States v. Macintosh, 283 U. S. 605, 626.
  The petitioner points out that in deportation cases this Court has held that an alien may not be expelled from this country on the ground that he has been a member of the Communist Party unless his participation in the Party amounted to “meaningful association.” Rowoldt v. Perfetto, 355 U. S. 115; Gastelum-Quinones v. Kennedy, 374 U. S. 469. He contends that the same rule should apply in the context of naturalization, and that the Government’s proof in this case failed to establish “meaningful association.” But the petitioner’s application was not denied because of his Communist Party membership. It was denied because, under oath, he did not tell the truth. The petitioner was not asked whether he had been “meaningfully associated” with the Communist Party. Nor was the inquiry limited to party membership. He was posed the much broader question whether he had ever “been a member of, or in any other way connected with, or associated with the Communist Party either directly, or indirectly through another organization, group, or person.” The District Court could rightly have found that the petitioner had not told the truth when he answered this question in the negative if he had not been an actual member, or his membership had been only nominal.
  Even assuming that an alien may be denied citizenship on the statutory ground of Party membership only when “meaningful association” is shown, the broader question asked of the petitioner was certainly material and relevant. The Government is entitled to know of any facts that may bear on an applicant’s statutory eligibility for citizenship, so that it may pursue leads and make further investigation if doubts are raised. The petitioner has never indicated that he was confused or misled by the scope of the question — that he believed at the time it was asked that the question reached only “meaningful association.”
  We cannot say that the District Court was wrong in finding that the petitioner had failed to tell the truth. It follows that the Court of Appeals was not in error in declining to upset that finding.
  Affirmed.
  Section 316 (a) of the Immigration and Nationality Act of 1952, 66 Stat. 242, 8 U. S. C. § 1427 (a), provides:
  “No person, except as otherwise provided in this title, shall be naturalized unless such petitioner, (1) immediately preceding the date of filing his petition for naturalization has resided continuously, after being lawfully admitted for permanent residence, within the United States for at least five years and during the five years immediately preceding the date of filing his petition has been physically present therein for periods totaling at least half of that time, and who has resided within the State in which the petitioner filed the petition for at least six months, (2) has resided continuously within the United States from the date of the petition up to the time of admission to citizenship, and (3) during all the periods referred to in this subsection has been and still is a person of good moral character, attached to the principles of the Constitution of the United States, and well disposed to the good order and happiness of the United States.”
  Section 101 (f), 66 Stat. 172, 8 U. S. C. § 1101 (f) :
  “For the purposes of this Act — No person shall be regarded as, or found to be, a person of good moral character who, during the period for which good moral character is required to be established, is, or was — ... (6) one who has given false testimony for the purpose of obtaining any benefits under this Act . . . ."
  Such an appearance is authorized by § 336 (d) of the Act, 66 Stat. 258, 8 U. S. C. § 1447 (d).
  239 F. Supp. 725.
  352 F. 2d 71. The Court of Appeals referred to Rule 52, Fed. Rules Civ. Proc., which provides in relevant part:
  “Findings by the Court, (a) Effect. . . . Findings of fact shall not be set aside unless clearly erroneous, and due regard shall be given to the opportunity of the trial court to judge of the credibility of the witnesses.”
  384 U. S. 903.
  A preliminary examination on the petitioner’s application for citizenship was held before a naturalization examiner, who transmitted his findings and recommendations to the District Judge, all pursuant to § 335 of the Act, 66 Stat. 255, 8 U. S. C. § 1446. But at the final hearing before the District Court, the judge heard testimony and conducted an independent hearing in accordance with §336 (b) of the Act, 66 Stat. 257, 8 U. S. C. §1447 (b), and explicitly declined to rely on any of the preliminary examination materials in reaching his conclusion. 239 F. Supp., at 727.
  At the same time, the judge found the evidence too weak to establish the Government’s alternative contention that the petitioner’s application should be denied because he had been a Party member within 10 years preceding his application for citizenship in 1962, and thus came within § 313 of the Act, 66 Stat. 240, 8 U. S. C. § 1424, which provides in relevant part:
  “'(a) ... no person shall hereafter be naturalized as a citizen of the United States—
  “(2) who is a member of or affiliated with . . . (D) the Communist or other totalitarian party ... of any foreign state ....
  “(c) The provisions of this section shall be applicable to any applicant for naturalization who at any time within a period of ten years immediately preceding the filing of the petition for naturalization or after such filing and before taking the final oath of citizenship is, or has been found to be within any of the classes enumerated within this section, notwithstanding that at the time the petition is filed he may not be included within such classes.”
  Schneiderman v. United States, 320 U. S. 118; Nowak v. United States, 356 U. S. 660; Chaunt v. United States, 364 U. S. 350.
  Woodby v. Immigration and Naturalization Service, ante, p. 276.
  The Government has not sought to deport the petitioner because of his affiliations with the Communist Party, and to do so it would be required to prove by “clear, unequivocal, and convincing evidence,” Woodby v. Immigration and Naturalization Service, supra, at 286, that the petitioner had been a Party member who was “meaningfully associated” with it, Rowoldt v. Perfetto, 355 U. S. 115; Gastelum-Quinones v. Kennedy, 374 U. S. 469. The Government’s evidence in this case fell clearly short of such a showing. Cf. n. 8, supra.
  The District Court specifically refused to accept the Government’s contention that the petitioner was ineligible for naturalization under the statutory provisions barring Communist Party members from citizenship. See n. 8, supra.
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