Senator Tom Cotton met in privare with Israeli Prime Minister Benjamin Netanyahu to discuss his opposition to the international nuclear agreement with Iran. Senator Cotton has been one of the most outspoken critics of the agreement, and signaled that he will side with Netanyahu over POTUS.
This is a violation of Chapter 115 - TREASON, SEDITION, AND SUBVERSIVE ACTIVITIES
Whoever incites, sets on foot, assists, or engages in any rebellion or insurrection against the authority of the United States or the laws thereof, or gives aid or comfort thereto, shall be fined under this title or imprisoned not more than ten years, or both; and shall be incapable of holding any office under the United States.
https://www.law.cornell.edu/uscode/text/18/part-I/chapter-115