Article III defines treason as either levying war against the United States or "adhering to their Enemies, giving them Aid and Comfort." The Supreme Court ruled in World War II cases that this second form of treason requires two elements: adherence to the enemy and rendering aid and comfort.
Justice Robert Jackson explained that actions might aid the enemy without constituting treason if there''s no intent to betray. The Constitution demands proof of two witnesses to the same overt act or a confession in open court for conviction. The Framers intentionally crafted this narrow definition to prevent the British practice of stretching treason charges to silence political opponents. Unlike many crimes Congress can define and redefine, the Constitution itself fixes what counts as treason, making it nearly impossible for the government to expand the offense to target dissent.