Does a court violate a criminal defendant's constitutional right to present a defense by excluding the strongest evidence supporting the sole theory of defense, simply because the evidence is circumstantial rather than direct and relies on reasonable inferences?

Under Davis v. Alaska, 415 U.S. 308 (1974), does a court violate the defendant's Sixth Amendment right to confrontation by making the cross-examination of witnesses about potential bias contingent on the witness first admitting an expected benefit and the benefit coming directly from the prosecution?

Does a court violate a criminal defendant's constitutional right to present a defense by excluding circumstantial evidence, and does limiting cross-examination about witness bias violate Sixth Amendment confrontation rights?