Is a witness who gives evidence at a joint trial considered a witness against a defendant if the jury is instructed to consider that testimony only against a codefendant?

"Ordinarily, a witness whose testimony is introduced at a joint trial is not considered to be a witness 'against' a defendant if the jury is instructed to consider that testimony only against a codefendant. This accords with the almost invariable assumption of the law that jurors follow their instructions . . . ." (Richardson v. Marsh, supra, 481 U.S. at p. 206.) However, " '[a] defendant is deprived of his Sixth Amendment right of confrontation when the facially incriminating confession of a nontestifying codefendant is introduced at their joint trial, even if the jury is instructed to

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