Whether, consistent with the Confrontation Clause, courts must apply a presumption favoring cross-examination of a government witness's general character for truthfulness, or whether courts may completely prohibit cross-examination that tests the witness's credibility or reliability without applying such a presumption?

Whether, consistent with the Confrontation Clause, courts must apply a presumption favoring cross-examination of a government witness's general character for truthfulness, or whether courts may completely prohibit cross-examination that tests the witness's credibility or reliability without applying such a presumption?