Article III Section 3

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.