Treason "Impossible"?

We all know about "Mission Impossible", but is "Treason Impossible" a similar fantasy?

Seems the esteemed Lawrence O'Donnell of MSNBC fame believes so since he continues to claim Treason is "impossible", apparently for anyone, as the US is not in a formal "state of war" and, thus, has no "Enemy". 

Certainly a finessing of the definition of Enemy as anyone of the "Cold War" era and Korean and Vietnam conflicts can attest.

Further, he asserts various Court cases have rendered such defining or supporting decisions, but has, thus far, never cited even ONE such case despite prodding to do so.