The bullet that felled Abraham Lincoln in 1865 made Andrew Johnson president. The new chief executive backed a plan for quickly reintegrating the former Confederate states into the Union. Congress’s more radical Republicans demanded stronger measures to punish rebellious states and protect the rights of freed slaves. The dispute boiled over when Johnson prepared to dismiss a cabinet member who had strong congressional support.

Overriding Johnson’s veto, Congress passed legislation denying the president’s power to remove officials without Senate consent. Johnson ignored the act, provoking impeachment by the House and a Senate trial. On May 16, 1868, seven Republican senators defied party leaders, voting with the 12 Democrats to acquit Johnson of “high crimes and misdemeanors”—by a one-vote margin. Ironically, Johnson returned to Washington in 1875 as a senator, the first former president to serve in the chamber.