Is a defendant required to prove his duress defense by a preponderance of the evidence?

Appellant also contends that the district court erred by instructing the jury that appellant must prove duress by a preponderance of the evidence.3 He claims that the district court should have instructed the jury that the government had to prove the absence of duress beyond a reasonable doubt. Appellant argues that the government should have born this burden because appellant would not have possessed the requisite mens rea if he had been acting under duress. "Whether a defendant has the burden of proving his duress defense by a preponderance of the evidence is a question of law which we review de novo." United States v. Meraz-Solomon, ³ F.3d 298, 299 (9th Cir. 1993) (per curiam).

We have stated that "[i]f a defense negates an element of the crime, rather than mitigates culpability once guilt is proven, it is unconstitutional to put the burden of proof on the defendant." Walker v. Endell, 850 F.2d 470, 472 (9th Cir. 1987). This is because "[d]ue process requires that the prosecution prove every

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