Former Members of Military, Who Improperly Try to Damage the President, Can Be Prosecuted Under a Number of Uniform Code of Military Justic Articles

http://www.ucmj.us/ 

Article 88, Contempt Towards Officials (Including the President)
Article 94, Mutiny or Sedition
Article 104, Aiding the Enemy
Article 107, False Statements

 
http://www.ucmj.us/sub-chapter-1-general-provisions/802-article-2-persons-subject-to-this-chapter