Basically, Theodore Roosevelt ran against William Taft in 1912 because he felt that Taft had deserted his (Roosevelt's) principles. Roosevelt had left the presidency believing that Taft would essentially be just like him. However, he felt that Taft's actions had been too conservative and not progressive enough. The most important things that Taft had done that annoyed Roosevelt were to fire Gifford Pinchot and to promote increased tariffs in the Payne-Aldrich Tariff bill. Because of these actions, Roosevelt felt that he needed to run again to get the country back on a more progresssive track.