Roosevelt's successor in 1908 was fellow Republican William Howard Taft. During the Taft administration, a rift grew between the two men, with the liberal Roosevelt (who favored land conservation, labor unions, and restrictions on the employment of women and children) becoming extremely disenchanted with the conservative Taft (who favored big business and judicial supremacy).
After failing to take the Republican nomination away from Taft at the 1912 GOP convention, Roosevelt formed his own party - the Progressive Party. (During a question and answer session with reporters, Roosevelt was asked how he felt. "I feel as strong as a bull mooose," he replied. And thus the Progressive Party also became known as the Bull Moose Party.)
Although Roosevelt couldn't stand the Democratic Party, his extremely successful second place finish granted Roosevelt his vendetta against President Taft and the Republicans. The Taft ticket came in third place, receiving an embarrassing 23% of the national popular vote and winning only two states (Utah and Vermont) equaling 8 votes in the Electoral College. The Progressive ticket won 27.5% of the vote and 88 electoral votes, and the Democratic ticket, led by Woodrow Wilson, won the election with 42% of the vote and a whopping 435 electoral votes.
Side note: While preparing to make a speech during a 1912 campaign stop in Milwaukee, Teddy Roosevelt was shot by a saloon-keeper named John Schrank. The bullet penetrated Roosevelt's chest, but was slowed by the steel eyeglass case and the 50 page folded copy of his speech that were in his coat pocket. Roosevelt, upon realizing the wound wasn't life threatening, told the crowd:
I don't know whether you fully understand that I have just been shot; but it takes more than that to kill a Bull Moose.He proceeded to give the entire speech as blood stained his shirt. Doctors later determined that it was too dangerous to remove the bullet, and Roosevelt carried it in him until he died.