18 USC 953 (the Logan Act):
"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."
The logan act does not apply here. Carter is going with approval and in fact encouragement of the white house. (I think they need drug testing with some of these guys). Carter is an idiot. I actually had a leftist teacher who loves him, but was honest enough to admit "he wasn't an effective president". She however defends him by saying he was ahead of his time, and everything that went wrong was the worlds fault. God some of these people are truely delusional. They honestly believe that the cause and purpose is more important then the results which cost american lives.