Treason was specifically defined in the United States Constitution, the only crime so defined. Article III Section 3 delineates treason as follows:
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.
However, Congress has, at times, passed statutes creating related offenses that undermine the government or the national security, such as sedition in the 1798 Alien and Sedition Acts, or espionage and sedition in the 1917 Espionage Act, which do not require the testimony of two witnesses and have a much broader definition than Article Three treason. For example, some well-known spies have been convicted of espionage rather than treason.”