What is the burden of proving that a witness was coerced at trial?

405, 452-453.) Defendant bears the burden of showing how the coercion " 'directly impaired the free and voluntary nature of the ... testimony in the trial itself [citation] and impaired the reliability of the trial testimony [citation]." (Id. at p. 453, fn. omitted.)²¹ "On appeal, we independently review the entire record to determine whether a witness's testimony was coerced, so as to render the defendant's trial unfair. [Citation.]" (People v. Boyer, supra, 38 Cal.4th at p. 444.)