Does substantial government interference with a defense witness's choice to testify amount to a violation of due process?

It is well established that "substantial government interference with a defense witness's free and unhampered choice to testify amounts to a violation of due process." United States v. Little, 753 F.2d 1420, 1438 (9th Cir.1984). A defendant alleging such interference is required to demonstrate misconduct by a preponderance of the evidence. See United States v. Lord, 711 F.2d 887, 891 n. 3 (9th Cir.1983). Whether substantial government interference occurred is a factual determination to be made by the district court that we review for clear error. See United States v. Baker, 10 F.3d 1374, 1415 (9th Cir.1993); Little, 753 F.2d at 1439.