Which U.S. President, known for his significant role in the post-Civil War era, faced an impeachment trial?

1. He succeeded Abraham Lincoln after his assassination.
2. He was a Democrat but was placed on the National Union ticket with a Republican to win the election.
3. His Reconstruction policies were in conflict with the Radical Republicans in Congress.
4. The Tenure of Office Act was passed during his presidency, leading to his impeachment.