Article III Section three of the constitution defines treason, grants Congress the power to create the offense of treason, and restricts the punishment to the person convicted of treason.
The crime of treason has been codified in 18 U.S. Code Section 2381.
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.
The critical word under treason law is “enemy.” In order for a nation to be an enemy of the United States, America must be in a declared or open war with that nation. An American working with Russia, for example, cannot be charged with treason because America is not at war with Russia. The Rosenbergs were convicted of espionage because America wasn’t at war with the Soviet Union when the Rosenbergs allegedly passed atomic secrets.
Under the Constitution, a person cannot be convicted of treason unless two witnesses to the act giving rise to the charge of treason testify, or the accused confesses in open court.
Only nine Americans have ever been convicted of treason.
Iva Toguri D’aquino, known as Tokyo Rose, is the only American citizen ever convicted of treason who was later pardoned. President Ford granted her pardon after it was discovered several witnesses at her trial lied.