In 1912, when Taft came up to be nominated by the Republicans, he was opposed by President Roosevelt who was disappointed with his actions in office. Roosevelt felt that Taft, whom he had handpicked, did not fulfill his vision for the presidency.

In the end, Roosevelt was defeated by Taft for the nomination and left the Republican party to form the Bull Moose party. Taft was then running against his former friend in addition to the Democratic candidate, Woodrow Wilson. Since both Taft and Roosevelt were pulling votes from Republicans, they ended up splitting the vote and allowing Wilson to win the election.

After retiring, Taft decided to teach law at Yale University from 1913 until 1921, but it was no secret that his ultimate goal was to become a Supreme Court justice. He got his wish in 1921 when President Warren G. Harding named him chief justice of the U.S. Supreme Court. One of his most famous decisions was for Olmstead v. United States, which found that the rule against unreasonable search and seizure did not apply to wiretapping. He served in this capacity until one month before his death on March 8, 1930. He was the only president to go on and become a Supreme Court justice. In fact, Taft viewed his time as a Supreme Court justice as his highest accomplishment.