Whether the Sixth Amendment permits joint representation of criminal codefendants as a general matter.
Holding
Yes. Joint representation is not per se unconstitutional, but it becomes constitutionally defective when counsel must represent conflicting interests.
Reasoning
The Court treated Glasser v. United States as establishing that the Sixth Amendment guarantees assistance of counsel that is free from conflicting loyalties. But Glasser did not prohibit every instance of one lawyer representing multiple defendants.
Joint representation may sometimes serve defendants' interests. Codefendants may have a common defense, and representation by one lawyer can prevent reciprocal blame. The constitutional problem arises when the lawyer's duties to one client diverge from duties to another.