The United States Constitution states in Article II, Section 4: “The President, Vice President and all 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.” *

*High Crimes and Misdemeanors refers to specific punishable offenses that apply to public officials, those who, “because of their official status, are under special obligations that ordinary persons are not under, and which could not be meaningfully applied or justly punished if committed by ordinary persons.”

Previous Presidents that endured impeachment proceedings:

In 1868 against President Andrew Johnson for his removal of Secretary of War Edwin Stanton ‘in violation of’ the Tenure of Office Act;

In 1974 implemented against President Richard M. Nixon for the Watergate cover up;

In 1998-99 implemented against President Bill J. Clinton for concealing an extramarital affair.

See: http://www.heritage.org/constitution/#!/articles/2/essays/100/standards-for-impeachment