1. In all states, this argument will be based upon the federal constitutional mandate that each defendant deserves a fair trial. The U.S. Supreme Court opinion that connects that fair trial guarantee with how a trial lawyer does (or doesn't) do his job is found in the case of Strickland v. Washington, 466 U.S. 668, 687 (1984).
2. If you want to know how your state's highest court has ruled regarding Strickland, then a free and easy way of roaming through the cases is to surf through Google Scholar (click on the Strickland link above) looking at cases heralding from your state (using Google Scholar advanced search).
Here, for example, is an opinion out of Florida's Fourth District Court of Appeal (not its highest court) in Aversano v. Florida, 966 So.2d 493, 494-495 (Fla. 4th DCA 2007):
First, the defendant must show that counsel’s performance was deficient. This requires showing that counsel made errors so serious that counsel was not functioning as the “counsel” guaranteed the defendant by the Sixth Amendment. Second, the defendant must show that the deficient performance prejudiced the defense. This requires showing that counsel’s errors were so serious that they deprived the defendant of a fair trial, a trial whose result is reliable. Strickland v. Washington, 466 U.S. 668, 687 (1984).
With rare exceptions, ineffective assistance of counsel claims should be raised in a motion for post-conviction relief because they are generally fact-specific. See Gore v. State, 784 So. 2d 418, 438 (Fla. 2001). “Only in cases where the incompetence and ineffectiveness of counsel is apparent on the face of the record and prejudice to the defendant is obvious do appellate courts address this issue on direct appeal.” McMullen v. State, 876 So.2d 589, 590 (Fla. 5th DCA 2004)(citations omitted).