Ineffective assistance of counsel is a claim raised by a convicted criminal defendant that their attorney's performance was so ineffective that it deprived them of the constitutional right guaranteed by the Assistance of Counsel Clause of the Sixth Amendment to the United States Constitution. Having the benefit of counsel or assistance of counsel means that the criminal defendant has had a competent attorney representing them. Competence is defined as reasonable professional assistance and is defined in part by prevailing professional norms and standards. In order to prevail on a claim that he received ineffective assistance, a criminal defendant must show two things:
Deficient performance by counsel.
Resulting prejudice, in that but for the deficient performance, the result of the proceeding would have differed.
Ineffective assistance of counsel may also be a ground for voiding a waiver of the right to appeal that a defendant may have signed as part of a plea agreement with prosecutors.
Under the two-prong Strickland standard, criminal convictions have been affirmed on appeal even where the defense attorney fell asleep during the prosecutor's cross-examination of the defendant, was heavily intoxicated on alcohol throughout the trial, was in extremely poor health and senile, was mentally ill (and even discussed his delusions in opening argument), or was himself a convicted felon whose sentence included community service in the form of defending accused murderers (despite his lack of experience in such cases).
The point of Strickland is that even extremely incompetent performance of counsel will not support a finding of ineffective assistance, if there was also independent and substantial evidence of the defendant's guilt, or if the end result would have probably been the same in the specific case even with a competent counsel.