civil officers of the United States, shall be removed from office on impeachment for, and conviction of treason, bribery, or other high crimes and misdemeanors.”
Some discussion:
http://www.crf-usa.org/impeachment/high-crimes-and-misdemeanors.html
I expect impeachment proceedings will get rolling sooner than later and probably this year. Because he refuses to consult anyone before acting on his illegal acts, has malignant narcissism, and thrives and seeks out conflict, it is unavoidable.