Until that year, presidential nominees were selected at conventions with delegates who were picked by party activists, office holders and leaders in proverbial smoke-filled backrooms. Even in states where the public could participate in some fashion, there was no way for voters to tell delegates which candidate to support.
At first Roosevelt did not support presidential primaries. In December, 1911, his supporters helped prevent the Republican National Committee from calling on states to adopt them. But once it became clear that Taft could control a convention where delegates were picked under the old rules, Roosevelt championed the new concept of presidential primaries. His campaign theme was “Let the People Rule.” He advocated controversial ideas and used inflammatory language to attack Taft, exciting crowds but throwing fear into the hearts of the leaders and business interests who still dominated the Republican Party.
The reform-minded Nation magazine said that Roosevelt's “violence of language, recklessness of assertion, and apparent inability to reason coherently make of him a spectacle disturbing to his friends and mortifying to the country.”
Many doubted the value of the new system. The New York Times called it “Party Suicide by Primary” and said it was “a first rate device for splitting a party wide open and inviting defeat on Election Day.” The old system may have been open to objection, it argued, “but for any electorate save one confined within the walls of an insane asylum, its advantages over this plan are obvious.”
Nevertheless, the primaries energized the public. TR won nine of the 13 newly created state contests and 70% of the popularly elected delegates. It wasn't enough to overcome the ability of the Republican Party leaders to manipulate the levers of power. Some recognized that Taft could not be reelected president, but they detested Roosevelt, and winning the White House mattered less to them than maintaining control of the party machinery
In a bitter convention, the Republicans nominated Taft who proceeded to come in third in the general election, trailing both Woodrow Wilson, the Democratic candidate, and TR who ran as the standard bearer of the Bull Moose Party, which he had created after being denied the Republican nomination.