D was charged with conspiracy to distribute more than 100 kilograms of marijuana. His family hired Fahle to represent him. After the arraignment, D called a California attorney, Joseph Low, to discuss whether Low would represent him, either in addition to or instead of Fahle. Low was hired. Low and Fahle appeared for D at an evidentiary hearing before a Magistrate Judge. The Magistrate Judge accepted Low’s provisional entry of appearance and permitted Low to participate in the hearing on the condition that he immediately file a motion for admission pro hac vice. During the hearing, the Magistrate revoked the provisional acceptance on the ground that, by passing notes to Fahle, Low had violated a court rule restricting the cross-examination of a witness to one counsel. D eventually informed Fahle that he wanted Low to be his only attorney. Low filed an application for admission pro hac vice. The District Court denied his application without comment. A month later, Low filed a second application, which the District Court again denied without explanation. Low’s appeal, in the form of an application for a writ of mandamus, was dismissed by the Court of Appeals for the Eighth Circuit. Fahle filed a motion to withdraw as counsel and for a show-cause hearing to consider sanctions against Low. Fahle claimed that Low violated Mo. Rule of Professional Conduct 4-4.2 (1993), which prohibits a lawyer “in representing a client” from “communicating about the subject of the representation with a party … represented by another lawyer” without that lawyer’s consent. Low filed a motion to strike Fahle’s motion. The District Court granted Fahle’s motion to withdraw and granted a continuance so that D could find new representation. D retained a local attorney, Karl Dickhaus, for the trial. The District Court then denied Low’s motion to strike and, for the first time, explained that it had denied Low’s motions for admission pro hac vice primarily because, in a separate case before it, Low had violated Rule 4-4.2 by communicating with a represented party. Dickhaus represented D at trial, and Low again moved for admission and was again denied. The Court also denied Dickhaus’s request to have Low at counsel table with him and ordered Low to sit in the audience and to have no contact with Dickhaus during the proceedings. A United States Marshal sat between Low and Dickhaus at trial. D was unable to meet with Low throughout the trial, except for once on the last night. D was convicted. The District Court granted Fahle’s motion for sanctions against Low. D appealed, and the Eighth Circuit vacated the conviction. The District Court erred in interpreting Rule 4-4.2 to prohibit Low’s conduct both in this case and in the separate matter on which the District Court based its denials of his admission motions. The Court then concluded that this Sixth Amendment violation was not subject to harmless-error review. P appealed.