Because the Tenure of Office Act did permit the president to suspend such officials when Congress was out of session , when Johnson failed to obtain Stanton 's resignation , he instead suspended Stanton on August 5 , 1867 , which gave him the opportunity to appoint General Ulysses S. Grant , then serving as Commanding General of the Army , interim Secretary of War . When the Senate adopted a resolution of non-concurrence with Stanton 's dismissal in December 1867 , Grant told Johnson he was going to resign , fearing punitive legal action . Johnson assured Grant that he would assume all responsibility in the matter , and asked him to delay his resignation until a suitable replacement could be found . Contrary to Johnson 's belief that Grant had agreed to remain in office , when the Senate voted and reinstated Stanton in January 1868 , Grant immediately resigned , before the president had an opportunity to appoint a replacement . Johnson was furious at Grant , accusing him of lying during a stormy cabinet meeting . The March 1868 publication of several angry messages between Johnson and Grant led to a complete break between the two . As a result of these letters , Grant solidified his standing as the frontrunner for the 1868 Republican presidential nomination
1868 Republican presidential nomination
1868 Republican National Convention
Impeachment of Andrew Johnson