It wasn't until T.R. returned from Africa in 1910 that he discovered how wrong he had been. Taft had none of T.R.'s energy, or his charisma. He didn't share much of T.R.'s vision, either. Taft dismissed Gifford Pinchot, T.R.'s conservation guru, from his post at the head of the Forest Service. He dissolved Roosevelt's cabinet, which he had earlier promised not to do. The final straw came when Taft tried to usurp Roosevelt's trust-busting legacy by criticizing Roosevelt for his relations with J.P Morgan. A furious Roosevelt wrote an angry article in The Outlook disputing Taft's claims and attacking the Taft administration's trust policies. Within days, the United States was abuzz with news of T.R.'s return to politics.
Roosevelt quickly positioned himself to challenge Taft for the Republican nomination in 1912. But the Roosevelt who sought a return to the presidency that year was not the young, New York politician chosen as McKinley's running mate more than a decade before. T.R. had become a bona-fide radical, with a reputation towering enough to risk challenging Republican Party orthodoxy directly. On the stump, Roosevelt preached outright wealth redistribution and true equality. He even started calling for women's suffrage! Roosevelt was unlike any Republican the Republican Party had ever seen.
His message found an audience. Roosevelt swept the Republican primaries. If the people had been in charge of choosing the Republican candidate, T.R. would almost certainly have been the nominee. But the 1912 nomination campaign was the first in American history to feature primaries at all, and only a few states used them to allow actual voters to have a say in determining each party's nominee. The bulk of the delegates who would actually select the presidential candidate were still chosen the old fashioned way: through machine-controlled caucuses and shady backroom deals. Taft exploited his entrenched position within the party (and many party bosses' horror at Roosevelt's maverick views) to secure his own renomination. William Howard Taft, not Teddy Roosevelt, was the Republican nominee for president in 1912.
T.R. refused to be stopped. He just left the party and kept campaigning. It's worth remembering that, in 1912, the idea of creating a third party wasn't that far-fetched. The Republicans, the dominant party throughout the Gilded Age, were less than sixty years old. Their founding as a radical third-party back in 1856 was still in living memory for many political veterans. Besides, T.R. realized that his reform agenda had widespread popular support, but neither the Democrats nor the Republicans really seemed interested in pursuing it. The night that Taft engineered his renomination, Roosevelt and his supporters met in a nearby hall, pledging themselves to found a new party to continue the fight for reform.
The Progressive Party, also known as the Bull Moose Party, was the most radical major party the United States had ever seen. It advocated for women's rights and called for universal suffrage. It demanded a fair minimum wage, and asked for old age insurance. In its policy proposals, it laid out what would eventually become the modern welfare state. At the party's convention that August, Jane Addams, the famed founder of Hull House, delivered T.R.'s seconding speech. Bull Moose supporters hailed from all walks of life—immigrants and elites, western ranchers and eastern city-dwellers. It wasn't surprising that someone tried to assassinate Roosevelt while he campaigned in Milwaukee. The kind of reform he was proposing made a lot of powerful people very uncomfortable.
Roosevelt's candidacy was a long shot, despite his popular support. The Democrats nominated Woodrow Wilson, a progressive governor and former Princeton University president, who appealed to many of T.R.'s more moderate backers. The Republican machine worked overtime to keep Taft in contention, even though their candidate lacked T.R.'s star power or Wilson's message. When the election results came in on 5 November 1912, Wilson claimed the presidency with a majority of the electoral vote and a plurality of the popular vote. A disheartened Roosevelt came in second. (Taft, for what it's worth, only carried Utah and Vermont.) Election night did what the assassin's bullet couldn't: it stopped the Bull Moose cold in his tracks.