What is the impeachment check in place history

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."

Thus far in the history of the United States there been three Presidential 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 - 1974 against President Richard Richard Nixon for the Watergate coverup (106 years after Johnson) - 1998-99 against President Bill Clinton for concealing an extramarital affair (24 years after Nixon).

b. 155 enlisted men and no officers