Article 3, Section 3 of the Constitution spells out what is considered treason in the United States: “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 the 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.”
Under this narrow definition there only have been about 30 treason trials in the United States since 1789. Prosecution under the federal treason statute is ultimately unlikely because "we are not at war with Russia". But during the Cold War, the treasonous conduct was often prosecuted under other statutes. In light of the Constitutional meaning of treason, we all, including politicians, need to be careful who we call a traitor. It could come back to bite you. :)