Only two U.S. Presidents have been impeached by the House of Representatives: Andrew Johnson and Bill Clinton. Both were acquitted in trials held by the Senate. In 1974, the House Judiciary Committee voted on Articles of Impeachment for Richard Nixon, but he resigned before the full House of Representatives voted on any of the articles.
Andrew Johnson was impeached on Feb. 24, 1868 for violating the Tenure of Office Act. He dismissed Edwin M. Stanton from office as the Secretary of War and replaced him with Major General Lorenzo Thomas without approval from the Senate.
Bill Clinton was impeached on Dec. 19, 1998 for charges of perjury and obstruction of justice relating to the Monica Lewinsky scandal.