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

The factors include [1] the importance of the witness's testimony in the prosecution's case,[2] whether the testimony was cumulative,[3] the presence or absence of evidence corroborating or contradicting the testimony of the witness on material points,[4] the extent of cross [-] examination otherwise permitted, and, of course,[5] the overall strength of the prosecution's case …

The Court held, however, that the "constitutionally improper denial of defendant's opportunity to impeach a witness for bias, like other Confrontation Clause errors, is subject to Chapman [v. California, 386 US 18, 87 S. Ct. 824, 17 L. Ed. 2d 705 (1967)] harmless error analysis."

"[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 …

The defendant must show that a reasonable jury might have received a significantly different impression of the witness's credibility had counsel been permitted to pursue his proposed line of cross-examination.

A] n 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

Indeed, on direct review of sixth amendment confrontation claims, the Supreme Court has held that constitutional error is not reversible error when it is "harmless."

The Sixth Amendment guarantees a defendant the right to cross-examine witnesses; it also allows a trial judge to place reasonable limits on cross-examination.