States can charge individuals with it, I'd assume mostly stemming from Civil War related nonsense (like someone else pointed out, John Brown was charged with treason by Virginia, not the US at large)

Colorado's statute on Treason

A person commits treason if he levies war against the state of Colorado or adheres to its enemies, giving them aid and comfort. No person shall be convicted of treason unless upon the testimony of two witnesses to the same overt act or upon confession in open court. Treason is a class 1 felony.

I'd think a fairly easy argument to make would be inciting revolt against US Congress fits the bill of 'adheres to enemies, giving aid and comfort', but we all know libs are scared to go the whole way against their fashy friends