https://en.wikipedia.org/wiki/Treason_laws_in_the_United_Sta...
Are you actually unaware he is getting contracts from DOD?
Slave rebellions
Puerto-Rican separatists
American citizens implicated in terrorism
The Congress has never even come close to declaring war in any of these circumstances.
One can also read it as: "moral treason", betrayal, etc. Not for talking with the guy, per se. But at the moment, if anyone is talking with Putin, it should be for one purpose only: to end the war -- and with that explicit framework in mind. Not business as usual of any kind.
And we shouldn't be expected to believe that they talked about “space as well as current and future technologies" in any case.
Though Elon is the kind of overachiever to possibly surmount a high bar, FARA might be a better bet.