In the 1983 case Strickland v. Washington, the U.S. Supreme Court established a two-part test to determine whether a defendant's Sixth Amendment right to counsel was violated due to ineffective assistance of counsel during their trial. The petitioner, David Leroy Washington, had pleaded guilty in Florida state court for three capital felonies and waived his rights to a jury trial without seeking any pretrial investigations or presenting mitigating evidence during sentencing hearing which resulted in death sentence for him. He later sought habeas corpus relief arguing that his attorney’s performance was deficient as he failed to move for psychiatric examination or present character witnesses at sentencing phase thus violating his constitutional right under Sixth Amendment. However, the Supreme Court held that not only must defendants prove their lawyer's performance fell below an objective standard of reasonableness (performance prong), but they also need to show there is reasonable probability that if it were not for these errors by counsel then outcome would have been different (prejudice prong). In this case, since Washington could not demonstrate prejudice resulting from alleged deficiencies in representation hence no violation of Sixth Amendment occurred.

In the dissenting opinion of Strickland v. Washington, Justice Thurgood Marshall argued that the majority's decision to establish a two-pronged test for ineffective assistance of counsel was too lenient and failed to adequately protect defendants' Sixth Amendment rights. He contended that any lawyer who fails to provide competent representation should be considered ineffective, regardless of whether their incompetence altered the outcome of the case. Furthermore, he criticized the majority's requirement for defendants to prove "prejudice" as part of their claim, stating it placed an unfair burden on them and could potentially allow grossly incompetent lawyers to continue practicing without repercussions if their clients couldn't definitively prove harm caused by poor representation. In essence, Marshall believed this ruling undermined constitutional guarantees for effective legal counsel in criminal cases.