In the case of Kimmelman, Attorney General of New Jersey, et al. v. Morrison (1985), the U.S. Supreme Court ruled that a criminal defendant's Sixth Amendment right to effective legal counsel was violated when his attorney failed to file a timely motion to suppress evidence obtained in an unconstitutional search and seizure operation by police officers. The court held that this failure constituted "ineffective assistance of counsel," even if it resulted from negligence rather than intentional misconduct on part of the defense lawyer. This decision expanded upon previous rulings regarding ineffective assistance claims under Strickland v Washington (1984) by recognizing that such claims could be based not only on errors affecting trial strategy but also those involving basic knowledge and understanding of constitutional law principles.

In the dissenting opinion for Kimmelman v. Morrison, Justice Powell argued that the majority's decision expanded the Sixth Amendment right to counsel beyond its intended scope. He contended that ineffective assistance of counsel should not be a basis for overturning a conviction unless it resulted in an unfair trial. In this case, he believed that there was no evidence suggesting Morrison did not receive a fair trial due to his attorney's failure to suppress illegally seized evidence. Furthermore, he asserted that allowing such claims could potentially open floodgates of litigation by defendants seeking new trials based on their attorneys' alleged incompetence or mistakes during pretrial proceedings rather than actual prejudice affecting their trials' outcomes.