In 1868 the House of Representatives resolved to adopt articles of impeachment against President Andrew Johnson because, it was contended, the president violated the Tenure of Office Act. This Act required Senate approval for removing certain office holders.
It was the contention of the House that the president violated this Act when he removed Edwin McMasters Stanton, the Secretary of War, from office and replaced him with Lorenzo Thomas.
The Tenure of Office Act, by the way, was only in effect from 1667 to 1887.
Did this violation by President Johnson truly warrant impeachment or was adopting articles of impeachment purely a political act by Congress? Your guess is as good as mime regarding this impeachment hearing, but of note President Johnson was not convicted by the Senate.