(Not to be confused with The Presidents of the United States of America)
Abraham Lincoln ← Andrew Johnson → Ulysses S. Grant
Andrew Johnson was the first US President to be impeached. He is generally considered to be one of the worst Presidents, though one could easily argue it's not entirely his fault. He was the only senator from a seceding state to remain pro-Union, so he was chosen as Lincoln's running mate to broaden the ticket's appeal and garner votes from Southern sympathizers. He was never intended to be anything other than a grab for votes. Then Lincoln got shot. Oops.
Johnson ended up breaking Jackson's previous record for most presidential vetoes. Obviously, the man didn't get along with Congress; they disagreed mightily about Reconstruction. Being a Southerner himself, Johnson wasn't going to penalize his own constituents too harshly. The Radical Republicans didn't much like this, and they kept competing until Congress finally passed the Tenure of Office Act, stating that the president couldn't fire any of his appointees without Congressional consent. The Radical Republicans knew Johnson would see this as a challenge to his authority, and violate it just to see what happened. He did when he fired Secretary of War Stanton, a Radical Republican raising havoc in Johnson's Cabinet. This was what they used to push through his impeachment.  Also, they sold tickets to the trial.
Johnson was acquitted by a single vote  and allowed to remain in office , but in the process, ended up losing pretty much all his political power. From that point until arguably the time of Theodore Roosevelt, Congress was effectively running the country rather than the office of the Presidency.
- Be Careful What You Wish For: The Radical Republicans wanted a President who would harshly punish the South, and they thought Lincoln was too soft,so when Johnson succeeded him, they were encouraged by his proclamations of doing just that. However Johnson never mentioned doing so on terms they agreed with, and in truth, he was happy to be even more forgiving than Lincoln, he just wanted the initial pleasure of making ex-Confederates grovel for mercy first.
- Book Dumb: Admitted he was until his wife taught him to read.
- Hidden Depths: Most of his clothes he made himself.
- Rags to Riches: Started out as a simple country tailor.
- Vitriolic Best Buds: At best, he was this to Lincoln, as he was a Southern sympathizer but a firm Unionist. Carried over to the Radical Republicans and Grant, until both realized the former meant much more to him than the latter.
- In 1887, the Tenure of Office Act was repealed by Congress, and subsequent rulings by the United States Supreme Court seemed to support Johnson's position that he was entitled to fire Stanton without Congressional approval. The Supreme Court's ruling on a similar piece of later legislation in the 1926 Myers v. United States affirmed the ability of the President to remove a Postmaster without Congressional approval, and stated in its majority opinion "that the Tenure of Office Act of 1867...was invalid"
- The lawyers defending Johnson, however, made the argument that Johnson never appointed Stanton: Lincoln did, and Johnson merely inherited Lincoln's Cabinet. Ergo, the Tenure of Office Act didn't apply to this case.
- The votes against impeachment were mostly from people who thought that the country had gone through enough turmoil and the complete defacing of the executive was a bad idea. There were also rumors of rampant bribery.