Johnson, the 17th president of the United States, was accused of violating the Tenure of Office Act. The 1867 required Senate approval before a president could remove any member of his cabinet who had been confirmed by the upper chamber of Congress.
The House impeached Johnson on February 24, 1868, three days after he dumped his secretary of war, a radical Republican named Edwin M. Stanton, allegedly in violation of the Tenure of Office Act. The U.S. Senate acquitted Johnson later that year by a narrow margin.
Be careful. I know about Johnson. But he wasn't elected president. He assumed the office upon Lincoln's death. My point was specifically tailored to one elected as president, in order to credit BJC with his due glory.