Which legal standard states that a defendant's actions must be a product of mental illness to establish a defense for insanity?

The correct answer is the Durham Rule, which establishes that a defendant may be excused from criminal liability if their unlawful act was a product of mental illness. This rule focuses on the relationship between mental illness and the defendant's actions, emphasizing that the mental disorder significantly influences their behavior, leading to the commission of the crime.

The Durham Rule arose from the case of Durham v. United States in 1954 and shifted the focus of the insanity defense from the defendant's ability to understand the nature of their acts (as considered in other standards) to whether the mental illness itself was the cause of the behavior.

In contrast, the Mens Rea refers to the intention behind a criminal act, which does not directly relate to the insanity defense. The Insanity Defense Reform Act established more stringent criteria for the insanity defense following notable cases where defendants used insanity pleas. The M'Naughten Rule, another significant legal standard for insanity, required that defendants could not understand the nature of their actions or distinguish right from wrong due to their mental disorder but does not specifically align with the idea of the actions being a product of mental illness, as emphasized by the Durham Rule.