The Logan Act, otherwise known as 18 U.S. Code § 953 – Private correspondence with foreign governments:
Any citizen of the United States, wherever he may be, who, without authority of the United States, directly or indirectly commences or carries on any correspondence or intercourse with any foreign government or any officer or agent thereof, with intent to influence the measures or conduct of any foreign government or of any officer or agent thereof, in relation to any disputes or controversies with the United States, or to defeat the measures of the United States, shall be fined under this title or imprisoned not more than three years, or both.
This section shall not abridge the right of a citizen to apply, himself or his agent, to any foreign government or the agents thereof for redress of any injury which he may have sustained from such government or any of its agents or subjects.
The ReThugs love show trials so much it would be worth it to prosecute Senator Tom Cotton, leader of the 47 Anti-Ronin, regardless of the fact the last (failed) attempt to enforce the law was way back in 1803.
I’d certainly attend, if only to throw spoiled tomatoes and other garbage at the defendant.
Hell, if nothing else charge him with Felony Stupid; that’s got to be covered in the U.S. Code somewhere, right?