Under the United States Constitution, there are two ways for someone who owes allegiance to the United States to commit treason:
(1) Levy war against the United States; or
(2) Give aid and comfort to an enemy of the United States.
Because of the interest in the letter recently sent by US Senators to the leaders of Iran with respect to ongoing nuclear weapons negotiations, today the focus is on "aid and comfort." Levying war will be the topic of another lesson.
The term "aid and comfort," generally, refers to acts that manifest a betrayal of allegiance to the United States, such as providing enemies with arms, troops, transportation, shelter, or classified information. If a subversive act has any tendency to weaken the power of the United States to attack or resist its enemies, aid and comfort has been given.
However, the "aid and comfort" clause applies only to disloyal acts committed during times of war. One who owes allegiance to the United States must be aiding a country or entity with whom the U.S. is actively at war.
The term "enemies" as used in the "aid and comfort" clause, according to its settled meaning when the Constitution was adopted, applies only to a foreign power in a state of open hostility with the United States -- that is, at war with the United States. This is well-settled law.
Here is the Constitutional provision that defines treason:
Treason against the United States, shall consist only in levying war against them, or in adhering to their enemies, giving them aid and comfort. No person shall be convicted of treason unless on the testimony of two witnesses to the same overt act, or on confession in open court.
The Congress shall have power to declare the punishment of treason, but no attainder of treason shall work corruption of blood, or forfeiture except during the life of the person attainted.
United States Constitution, Article III, Section 3
Treason was covered in the US Constitution not to create the offense but to restrict its definition. The founders were wary of the concept of treason, which in their view had been misused by English monarchs.
Here is the federal statute that makes treason a crime:
18 U.S. Code § 2381 - Treason
Whoever, owing allegiance to the United States, levies war against them or adheres to their enemies, giving them aid and comfort within the United States or elsewhere, is guilty of treason and shall suffer death, or shall be imprisoned not less than five years and fined under this title but not less than $10,000; and shall be incapable of holding any office under the United States.