Although Johnson had no official White House pet, he was known to feed a family of white mice that had taken up residence in his bedroom. During his impeachment, he remained secluded in the White House, entertaining himself with the mice. He would leave water out for the family to drink and watch their antics while he waited for the decision to come down from the Senate. He claimed to have won the mice's confidence and often called them "the little fellows."

Johnson was at odds with Congress for most of his presidency, resulting in a then-record 29 vetoes, 15 of which were overridden by Congress.

Johnson received some support for another term at the 1868 Democratic National Convention, but after several ballots, the convention nominated Horatio Seymour, who had formerly served as Governor of New York. In the general election, Seymour was easily defeated by Republican Ulysses S. Grant.

Following his departure from the White House in 1869, Johnson served in the U.S. Senate--the only president ever to do so following his presidential term--before succumbing to a stroke in July 1875.