Article III, Section 3: from Legal Information Institute [1]:
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.
The British had a rather low definition of treason. For example, if you denied that God gave King George the right to rule over you, you were guilty of Treason. The Founding Fathers did not approve of such a whimsical definition, and codified a much higher definition, see above.
Evidently, if media/liberal complex ever read the Constitution, they don’t remember it. Note one John Brennan. a man who admitted to voting for a communist for President, from Investor’s Business Daily [2]:
Former CIA Director John Brennan, in particular, sounded like someone in need of intervention in his tweet: “Donald Trump’s press performance in Helsinki rises to & exceeds the threshold of ‘high crimes and misdemeanors. It was nothing short of treasonous. Not only were Trump’s comments imbecilic, he is wholly in the pocket of Putin. Republican Patriots: Where are you???”
So maybe the Brennan standard, such as it is, holds that while it is permissible to vote for a communist it is treasonous to actually talk to one.