I agree with the other posters: the GOP was split right down the middle with each side wanting the other to win. Both thought they could, but ultimately it was Taft's conservatives who were in control of the party machinery and thus narrowly beat Roosevelt even though he was actually more popular. This is what began the GOP's transformation into the party of conservatism, a process which was complete by the time TR's younger cousin finished his tenure in the White House. Republicans were still more liberal on social issues until 1964, but even then Dewey, Warren, Ike, and Rockefeller all self-identified as fiscal conservatives. But I digress. My point is that 1912 was such a critical flashpoint in the history of the Republican Party that unity was impossible, even if TR had jumped into the race earlier and/or gotten LaFollette's endorsement as many historians say he should. Roosevelt was never going to be the nominee that year unless Taft stepped down and endorsed him for whatever ASB reason. The Republican elites hated TR from the very beginning of his political career and actively worked to sabotage him as President. In fact the very reason he become Chief Exec in 1901 was because he was made VP first, and only because party bosses were trying to get rid of him. Scratch that, destroy him. And in 1912 they finally succeeded. Roosevelt would never tolerate that and his only option was to run third party even if he lost.