The Radical Republicans in Congress differed with Andrew Johnson about how deeply the federal government would be involved in changing southern governments and southern society after the Civil War during the period called Reconstruction. Johnson, who was from Tennessee, was considered too soft on the former Confederate states. For example, he agreed to permit state governments to grant amnesty to former rebels. He angered the Radical Republicans in Congress by refusing to recharter the Freedman's Bureau in 1866. The Freedman's Bureau was intended to help former slaves find family members and receive other services, such as education. In addition, some southern states enacted laws called Black Codes that limited freed slaves' movements, tied them to plantations, and restricted their other civil rights; nonetheless, Johnson vetoed the Civil Rights Act of 1866 that would have been a mitigating force against the Black Codes. He believed these bills were an infringement on states' rights, and he also opposed the 14th Amendment, which granted former slaves citizenship and due process rights (as he wanted the Confederate states to be restored to the Union before new Constitutional amendments were passed).

To curb Johnson's power, Congress enacted the Tenure of Office Act in 1867, which limited the President's power to remove office holders. This act was likely unconstitutional, and it was later amended and then repealed entirely in 1887. The Tenure of Office Act was passed over Johnson's veto. When Johnson tried to remove Edwin Stanton, the Secretary of War and a Radical Republican, in August of 1867, the House initiated impeachment proceedings against Johnson in January of 1868. He was the first President to be impeached in American history. The Senate conducted a three-month trial, and Johnson was acquitted by a single vote.

The Radical Republicans had several reasons for wanting to impeach President Andrew Johnson.  Andrew Johnson and the Radical Republicans had clashed over Reconstruction. Andrew Johnson had a plan that the Radical Republicans thought was too easy on the South.  As a result, Johnson turned on the Radical Republicans. He vetoed a bill that would have given the Freedmen’s Bureau more money as well as the Civil Rights Act of 1866. He even campaigned against Republicans in the mid-term elections of 1866.  Thus, the Radical Republicans were looking for a way to get rid of President Johnson.

Congress passed the Tenure of Office Act in 1867. It prevented the president from removing a government official such as a cabinet member without the approval of the Senate. Johnson felt this law was unreasonable and a form of political payback.  When he fired the Secretary of War, Edwin Stanton, without the approval of the Senate, the House of Representatives impeached him.  While he was impeached, he was not removed from office as the Senate fell one vote short of removing him.

Why did Republicans in Congress want to impeach Andrew Johnson?

The Radical Republicans in Congress felt that Andrew Johnson, a southerner, was too easy on the south during Reconstruction. The Republicans in Congress, such as Thaddeus Stevens and Charles Sumner, wanted to radically reform the south to abolish the old planter class, while Johnson's plan for Reconstruction was more lenient.

The Republicans watched as the Black Codes were instituted in states such as Mississippi; these laws prevented the free movement of former slaves and abridged some of their other civil rights. In response, the Republicans wanted to pass the Civil Rights Act of 1866, but Johnson vetoed it, saying that it infringed on states' rights. In addition, in 1866, Johnson vetoed the bill to renew chartering for the Freedmen's Bureau (founded in 1865), which had provided assistance to former slaves such as finding family members, education, and the promotion of fair labor contracts between former slaves and plantation owners. Johnson also dissuaded states from passing the 14th Amendment, which gave citizenship and due process rights to African-American people.

As a result of these feuds, the Congress passed the Tenure of Office Act in 1867, which limited Johnson's power to remove cabinet members. When he removed Secretary of War Stanton, who was a member of the Radical Republicans, the House moved to have Johnson impeached. He was saved by conviction in the Senate by a single vote.