This legislation addresses for the first time how the insanity defense should be used in federal insanity trials. A bill was proposed to allow claims of insanity to be raised only to rebut the prosecution's contention that a given defendant had the requisite mens rea, or culpable mind, required for conviction. Supporters of this reform praised it on the grounds that only those so insane they literally did not know what they were doing when they committed their crimes could be acquitted. However, Congress eventually abandoned the mens rea approach because it was considered too extreme a narrowing of the defense and might be difficult for the prosecution to prove. In future federal cases defendants will have to prove by "clear and convincing evidence" that they could not appreciate the wrongfulness of their conduct. If they are unable to do this, their insanity defenses will fail.