opinion: Justice Rehnquist
  delivered the opinion of the Court.
  Respondent Robert Van Arsdall was convicted of murder in a Delaware trial court. The Supreme Court of Delaware reversed his conviction on the ground that the trial court, by improperly restricting defense counsel’s cross-examination designed to show bias on the part of a prosecution witness, had violated respondent’s confrontation rights under the Sixth and Fourteenth Amendments to the United States Constitution, and that such violation required automatic reversal. 486 A. 2d 1 (1984). While we agree that the trial court’s ruling was contrary to the mandate of the Confrontation Clause of the Sixth Amendment, we conclude that the Supreme Court of Delaware was wrong when it declined to consider whether that ruling was harmless in the context of the trial as a whole.
  Shortly after midnight on January 1, 1982, Doris Epps was stabbed to death in an apartment in Smyrna, Delaware, after an all-day New Year’s Eve party. Respondent and Daniel Pregent, who by respondent’s testimony were the only two people in the apartment with Epps at the time she was killed, were arrested at the scene of the crime and charged with Epps’ murder. At separate trials, respondent was convicted and Pregent was acquitted.
  The State’s case against respondent was based on circumstantial evidence, and proceeded on the theory that respondent had either killed Epps or assisted Pregent in doing so. Several of the partygoers testified about the party and the scene after the killing. The party, which lasted from late in the morning of December 31, 1981, until shortly before midnight, was held in the adjacent apartments of Pregent and Robert Fleetwood. Respondent, who was one of at least a dozen guests who attended the party during the course of the day, had stopped in for two brief periods in the late afternoon and early evening and then returned for a third time at about 11:30 p.m. By that time the party was over. Pregent had quarreled with a female guest, kicked a hole in a hallway wall and had to be restrained. An intoxicated Epps had been placed on a sofa bed in Pregent’s apartment after passing out. And shortly before 11 p.m., a second altercation of some kind occurred, prompting Fleetwood to close the party in his apartment to everyone except his two friends, Alice Meinier and Mark Mood. When respondent returned to Pregent’s apartment at about 11:30, only Pregent and Epps were present.
  Robert Fleetwood was the 10th of 16 prosecution witnesses. In addition to recounting uncontroverted facts about the party, he testified that sometime between 11 and 11:30 p.m. he walked across the hall, looked into Pregent’s living room from the doorway, and saw respondent sitting on the edge of the sofa bed next to Pregent’s feet. Fleetwood, who did not have a complete view of the bed, did not see Epps or anyone else in the apartment. Upon returning to his own apartment, Fleetwood stayed awake long enough to hear nearby bells ring in the New Year, at which point he passed out. App. 82-85.
  Meinier, who with Mood had remained awake in Fleet-wood’s apartment, testified that at roughly 1 a.m. respondent knocked at Fleetwood’s door. Respondent’s shirt and hands were spattered with blood, and he was holding a long, blood-covered knife. According to Meinier, respondent stated that “he had gotten in a fight” but that he “got them back.” Id., at 130. After turning the knife over to Mood and washing his hands, respondent said “I think there’s something wrong across the hall.” Id., at 132. Meinier went to Pregent’s apartment and discovered Epps’ body lying in a pool of blood on the kitchen floor. Mood then summoned the police, who found respondent in Fleetwood’s apartment and Pregent asleep on the blood-splattered sofa bed in his living room.
  In addition to the testimony of the partygoers and the arresting officers, the State introduced Pregent’s postarrest statement, respondent’s two postarrest statements, and the testimony of a forensic expert. Among other things, the expert testified about the nature and source of the bloodstains on respondent’s clothing.
  During Fleetwood’s cross-examination, defense counsel sought to impeach Fleetwood by questioning him about the dismissal of a criminal charge against him — being drunk on a highway — after he had agreed to speak with the prosecutor about Epps’ murder. When the prosecutor objected, the trial court allowed counsel to question Fleetwood on the matter outside the presence of the jury. Fleetwood acknowledged that the drunkenness charge had been dropped in exchange for his promise to speak with the prosecutor about the murder, but he denied that the agreement had affected his testimony. The trial court barred any cross-examination about that agreement, citing Delaware Rule of Evidence 403. The court also refused to permit defense counsel to cross-examine Fleetwood about his being questioned by the police in connection with an unrelated homicide that had occurred after Epps’ murder. On voir dire conducted outside the presence of the jury, Fleetwood denied that he had been offered any favors, inducements, promises, or deals concerning that homicide investigation in exchange for his testimony at respondent’s trial.
  Respondent was the only defense witness. Consistent with his second statement to the police, he attributed Epps’ murder to Pregent. Consistent with Fleetwood’s testimony, he stated that he had returned to Pregent’s apartment, after drinking with friends, by about 11:30 p.m.
  Defense counsel admitted in their opening and closing arguments to the jury that respondent was in Pregent’s apartment when Epps was killed. In closing argument, after attempting to discredit Fleetwood’s testimony (largely by emphasizing his intoxication), counsel stressed that all that testimony proved was what respondent “never denied,” that “he was at Danny Pregent’s apartment before Doris Epps was murdered.” App. 188-189. The jury found respondent guilty of first-degree murder and possession of a deadly weapon during the commission of a felony.
  bn appeal, the Delaware Supreme Court reversed respondent’s conviction on the authority of the Confrontation Clause. Noting that “the bias of a witness is subject to exploration at trial and is ‘always relevant as discrediting the witness and affecting the weight of his testimony,”’ 486 A. 2d, at 6 (quoting Davis v. Alaska, 415 U. S. 308, 316 (1974)), the court found that the trial judge’s ruling denied respondent his constitutional right to effective cross-examination. By barring any cross-examination of Fleetwood about the dismissal of the public drunkenness charge, the ruling kept from the jury facts concerning bias that were central to assessing Fleetwood’s reliability. The court rejected the State’s argument that since “Fleetwood’s basic testimony was cumulative in nature and unimportant,” the Confrontation Clause error was harmless beyond a reasonable doubt. 486 A. 2d, at 7. The court held that “a blanket prohibition against exploring potential bias through cross-examination” is “a per se error,” so that “the actual prejudicial impact of such an error is not examined.” Ibid.
  We granted certiorari, 473 U. S. 923 (1985), and now vacate and remand.
  The Confrontation Clause of the Sixth Amendment guarantees the right of an accused in a criminal prosecution “to be confronted with the witnesses against him.” The right of confrontation, which is secured for defendants in state as well as federal criminal proceedings, Pointer v. Texas, 380 U. S. 400 (1965), “means more than being allowed to confront the witness physically.” Davis v. Alaska, 415 U. S., at 315. Indeed, “‘[t]he main and essential purpose of confrontation is to secure for the opponent the opportunity of cross-examination.’” Id., at 315-316 (quoting 5 J. Wig-more, Evidence § 1395, p. 123 (3d ed. 1940)) (emphasis in original). Of particular relevance here, “[w]e have recognized that the exposure of a witness’ motivation in testifying is a proper and important function of the constitutionally protected right of cross-examination.” Davis, supra, at 316-317 (citing Greene v. McElroy, 360 U. S. 474, 496 (1959)). It does not follow, of course, that the Confrontation Clause of the Sixth Amendment prevents a trial judge from imposing any limits on defense counsel’s inquiry into the potential bias of a prosecution witness. On the contrary, trial judges retain wide latitude insofar as the Confrontation Clause is concerned to impose reasonable limits on such cross-examination based on concerns about, among other things, harassment, prejudice, confusion of the issues, the witness’ safety, or interrogation that is repetitive or only marginally relevant. And as we observed earlier this Term, “the Confrontation Clause guarantees an opportunity for effective cross-examination, not cross-examination that is effective in whatever way, and to whatever extent, the defense might wish.” Delaware v. Fensterer, 474 U. S. 15, 20 (1985) (per curiam) (emphasis in original).
  In this case, however, the trial court prohibited all inquiry into the possibility that Fleetwood would be biased as a result of the State’s dismissal of his pending public drunkenness charge. By thus cutting off all questioning about an event that the State conceded had taken place and that a jury might reasonably have found furnished the witness a motive for favoring the prosecution in his testimony, the court’s ruling violated respondent’s rights secured by the Confrontation Clause.
  The State somewhat tentatively suggests that a defendant should have to show “outcome determinative” prejudice in order to state a violation of the Confrontation Clause: Unless the particular limitation on cross-examination created a reasonable possibility that the jury returned an inaccurate guilty verdict, that limitation would not violate the Confrontation Clause. We disagree. While some constitutional claims by their nature require a showing of prejudice with respect to the trial as a whole, see, e. g., Strickland v. Washington, 466 U. S. 668 (1984) (ineffective assistance of counsel), the focus of the Confrontation Clause is on individual witnesses. Accordingly, the focus of the prejudice inquiry in determining whether the confrontation right has been violated must be on the particular witness, not on the outcome of the entire trial. It would be a contradiction in terms to conclude that a defendant denied any opportunity to cross-examine the witnesses against him nonetheless had been afforded his right to “confrontation]” because use of that right would not have affected the jury’s verdict. We think that a criminal defendant states a violation of the Confrontation Clause by showing that he was prohibited from engaging in otherwise appropriate cross-examination designed to show a prototypical form of bias on the part of the witness, and thereby “to expose to the jury the facts from which jurors . . . could appropriately draw inferences relating to the reliability of the witness.” Davis v. Alaska, supra, at 318. Respondent has met that burden here: A reasonable jury might have received a significantly different impression of Fleetwood’s credibility had respondent’s counsel been permitted to pursue his proposed line of cross-examination.
  After concluding that the trial judge’s ruling was constitutional error, the Delaware Supreme Court rebuffed the State’s effort to show “beyond a reasonable doubt that the error complained of did not contribute to the verdict obtained,” Chapman v. California, 386 U. S. 18, 24 (1967). In so doing, it offered no explanation why the Chapman harmless-error standard, which we have applied in other Confrontation Clause cases, e. g., Harrington v. California, 395 U. S. 250 (1969); Schneble v. Florida, 405 U. S. 427 (1972), is inapplicable here. We find respondent’s efforts to defend the automatic reversal rule unconvincing.
  As we have stressed on more than one occasion, the Constitution entitles a criminal defendant to a fair trial, not a perfect one. E. g., United States v. Hasting, 461 U. S. 499, 508-509 (1983); Bruton v. United States, 391 U. S. 123, 135 (1968). In Chapman, this Court rejected the argument that all federal constitutional errors, regardless of their nature or the circumstances of the case, require reversal of a judgment of conviction. The Court reasoned that in the context of a particular case, certain constitutional errors, no less than other errors, may have been “harmless” in terms of their effect on the factfinding process at trial. Since Chapman, we have repeatedly reaffirmed the principle that an otherwise valid conviction should not be set aside if the reviewing court may confidently say, on the whole record, that the constitutional error was harmless beyond a reasonable doubt. E. g., United States v. Hasting, supra (improper comment on defendant’s silence at trial); Moore v. Illinois, 434 U. S. 220, 232 (1977) (admission of identification obtained in violation of right to counsel); Harrington v. California, supra (admission of nontestifying codefendant’s statement). The harmless-error doctrine recognizes the principle that the central purpose of a criminal trial is to decide the factual question of the defendant’s guilt or innocence, United States v. Nobles, 422 U. S. 225, 230 (1975), and promotes public respect for the criminal process by focusing on the underlying fairness of the trial rather than on the virtually inevitable presence of immaterial error. Cf. R. Traynor, The Riddle of Harmless Error 50 (1970) (“Reversal for error, regardless of its effect on the judgment, encourages litigants to abuse the judicial process and bestirs the public to ridicule it”).
  At the same time, we have observed that some constitutional errors — such as denying a defendant the assistance of counsel at trial, or compelling him to stand trial before a trier of fact with a financial stake in the outcome — are so fundamental and pervasive that they require reversal without regard to the facts or circumstances of the particular case. Chapman, supra, at 23, n. 8 (citing, inter alia, Gideon v. Wainwright, 372 U. S. 335 (1963), and Turney v. Ohio, 273 U. S. 510 (1927)). The error at issue here is obviously quite different, however, as this Court’s post -Chapman decisions demonstrate. In Harrington v. California, for example, we expressly rejected the claim that the admission into evidence of a statement made by a nontestifying codefendant, in violation of Bruton v. United States, supra, can never be harmless. Harrington, which we have expressly reaffirmed on more than one occasion, see, e. g., Schneble v. Florida, supra; Brown v. United States, 411 U. S. 223 (1973), demonstrates that the denial of the opportunity to cross-examine an adverse witness does not fit within the limited category of constitutional errors that are deemed prejudicial in every case.
  Respondent seeks to blunt the force of Harrington in essentially two ways. First, he suggests that this Court’s decision in Davis v. Alaska forecloses application of harmless-error analysis to the particular sort of Confrontation Clause violation involved here, citing the following language near the end of the Court’s opinion:
  “[Davis] was thus denied the right of effective cross-examination which ‘ “would be constitutional error of the first magnitude and no amount of showing of want of prejudice would cure it.” Brookhart v. Janis, 384 U. S. 1, 3.’” 415 U. S., at 318 (quoting Smith v. Illinois, 390 U. S. 129, 131 (1968)).
  Read properly, however, Davis does not support an automatic reversal rule, and the above-quoted language merely reflects the view that on the facts of that case the trial court’s error had done “serious damage” to the petitioner’s defense.
  Davis was charged with stealing a safe from a bar. The police found the stolen safe abandoned near the home of Richard Green, who testified at trial that he had seen Davis engaged in suspicious activity near this site on the day of the crime. Defense counsel was barred from eliciting on cross-examination that Green was on juvenile probation for burglary both at the time of his pretrial identification of Davis and at the time of trial. The defense sought to suggest that Green may have slanted his account in the State’s favor either to shift suspicion away from himself or to avoid revocation of probation for failing to “cooperate.” 415 U. S., at 310-311. This Court reversed Davis’ conviction, emphasizing that Green’s tesimony was “crucial” and that there was a “real possibility” that pursuit of the excluded line of impeachment evidence would have done “[sjerious damage to the strength of the State’s case.” Id., at 319. So despite the absence of a reference to Chapman, Davis plainly rests on the conclusion that on the facts of that case, the error might well have contributed to the guilty verdict. Davis should not be read as establishing, without analysis, a categorical exception to the harmless-error rule.
  Respondent’s second argument in support of a per se reversal rule is that the Confrontation Clause error in this case, which like Davis involved the exclusion of evidence, is analytically distinct from that in Harrington v. California, which involved the erroneous admission of harmless testimony. Because it is impossible to know how wrongfully excluded evidence would have affected the jury, the argument runs, reversal is mandated. But Harrington cannot be so easily dispatched. Respondent, like Harrington, was denied an opportunity to cast doubt on the testimony of an adverse witness. In both cases the prosecution was thus able to introduce evidence that was not subject to constitutionally adequate cross-examination. And in both cases the reviewing court should be able to decide whether the not-fully-impeached evidence might have affected the reliability of the factfinding process at trial.
  Accordingly, we hold that the constitutionally improper denial of a defendant’s opportunity to impeach a witness for bias, like other Confrontation Clause errors, is subject to Chapman harmless-error analysis. The correct inquiry is whether, assuming that the damaging potential of the cross-examination were fully realized, a reviewing court might nonetheless say that the error was harmless beyond a reasonable doubt. Whether such an error is harmless in a particular case depends upon a host of factors, all readily accessible to reviewing courts. These factors include the importance of the witness’ testimony in the prosecution’s case, whether the testimony was cumulative, the presence or absence of evidence corroborating or contradicting the testimony of the witness on material points, the extent of cross-examination otherwise permitted, and, of course, the overall strength of the prosecution’s case. Cf. Harrington, 395 U. S., at 254; Schneble v. Florida, 405 U. S., at 432.
  We believe that the determination whether the Confrontation Clause error in this case was harmless beyond a reasonable doubt is best left to the Delaware Supreme Court in the first instance. Accordingly, that court’s judgment is vacated, and the case is remanded for further proceedings not inconsistent with this opinion.
  It is so ordered.
  When asked about his understanding of why the charge was dropped, respondent stated:
  “Well, I did understand that I did feel that you wanted to make sure that I knew what I was talking about and I do feel that you wanted to make sure I had my story together before coming in here. So that is why I did feel that it was dropped.” App. 106.
  Delaware Rule of Evidence 403, which is virtually identical to Federal Rule of Evidence 403, provides:
  “Although relevant, evidence may be excluded if its probative value is substantially outweighed by the danger of unfair prejudice, confusion of the issues or misleading the jury, or by considerations of undue delay, waste of time or needless presentation of cumulative evidence.”
  Respondent asserts that this Court is without jurisdiction to hear this case because the Delaware Supreme Court’s automatic reversal rule rests on an adequate and independent state ground. He argues that the rule was adopted not on the basis of federal constitutional law but as a prophylactic device, announced under that court’s “superintending” authority, to “send an unequivocal message” to state trial judges about the importance of permitting liberal cross-examination. Brief for Respondent 41. We disagree.
  “[W]e will not assume that a state-court decision rests on adequate and independent state grounds when the ‘state court decision fairly appears to rest primarily on federal law, or to be interwoven with the federal law, and when the adequacy and independence of any possible state law ground is not clear from the face of the opinion.’” Caldwell v. Mississippi, 472 U. S. 320, 327 (1985) (quoting Michigan v. Long, 463 U. S. 1032, 1040-1041 (1983)). The opinion of the Delaware Supreme Court, which makes use of both federal and state eases in its analysis, lacks the requisite “plain statement” that it rests on state grounds. Michigan v. Long, supra, at 1042, 1044. Indeed, the opinion makes no reference to any “superintending” authority, and nowhere suggests the existence of a state prophylactic rule designed to insure protection for a federal constitutional right. We read the decision below as resting on federal law.
  The Delaware Supreme Court did not decide whether the trial court erred in preventing respondent from cross-examining Fleetwood about the unrelated homicide investigation. 486 A. 2d 1, 7, n. 3 (1984). We likewise decline to consider that question.
  Bruton had held that the receipt at a joint trial of the incriminating statement of a nontestifying codefendent deprived Bruton of his right to cross-examine an adverse witness. In Harrington, the trial court admitted the pretrial statements of two codefendants who did not testify. The statements implicated Harrington by placing him at the scene of the robbery, and their admission plainly violated Bruton. This Court nevertheless affirmed Harrington’s conviction, over his objection that Bruton error could never be harmless. Noting that the wrongfully admitted evidence was cumulative and that the untainted proof of the defendant’s guilt was overwhelming, the Court concluded that the error was harmless beyond a reasonable doubt. 395 U. S., at 254.
  Respondent does not contend that he was denied the opportunity to elicit exculpatory evidence from Fleetwood.
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