The Sixth Amendment guarantees a criminal defendant "the assistance of counsel for his defence." The Supreme Court has interpreted that right to include the effective assistance of counsel. However, a judgment cannot be overturned on the ground of ineffective counsel unless, in addition to the lawyer being ineffective, the defendant makes a showing of resulting "prejudice." The meaning of "prejudice" in various circumstances has been the subject of a lot of cases since the high court established that standard in 1984.
The purpose of the Sixth Amendment is to guarantee a fair trial. If the defendant does indeed receive a fair trial, can he get the judgment overturned on the theory that a better lawyer would have gotten him a plea bargain? That idea seems strange, given that there is no right to a plea bargain and that the defendant received the fair trial the Constitution entitles him to. We took that position in an amicus brief in Lafler v. Cooper, 566 U.S. 156 (2012). Four justices agreed with us, but five did not.
Judge Gorsuch took the same position as the Lafler dissenters three years earlier in the case of Williams v. Jones, 571 F.3d 1086 (2009). Williams was a murderer, but there is no discussion of the facts in the opinion. Judge Gorsuch's dissent says, "The Sixth Amendment right to effective assistance of counsel is an instrumental right designed to ensure a fair trial. By his own admission, Michael Williams received just such a trial, at the end of which he was convicted of first degree murder by a jury of his peers. We have no authority to disturb this outcome."
I think he was right. In any case, this opinion is well within the mainstream, as indicated by the 5-4 split in the Supreme Court.