When it comes to mounting independent challenges to the two-party system in American politics, Theodore Roosevelt and Ross Perot have been the most successful since 1900. While every presidential election features independent candidates, they generally lack the standing even to garner invitations to debates.
Theodore Roosevelt became President upon the assassination of William McKinley in 1901 and won re-election in 1904. When his hand-picked successor, William Howard Taft, failed to follow Roosevelt's philosophy, Roosevelt ran against his protege in 1912. Taft earned the Republican nomination, so Roosevelt mounted his own effort, calling it the Progressive Party and giving it the mascot of a bull moose. He won 27 percent of the popular vote and 88 electoral votes, stealing enough of Taft's support to deliver the election to Democrat Woodrow Wilson.
In 1992, Ross Perot created the Reform Party as an independent campaign. Inexplicably, he dropped out of the contest before Bill Clinton earned the Democratic nomination. He re-entered, but much of his previous support had evaporated. Even so, he won 18.9 percent of the popular vote but not enough in any state to carry any electoral votes.
Robert La Follette (1924) and George Wallace (1964) are the only other independent candidates who gained electoral votes since 1900. Their predominantly regional appeal (La Follette in the Midwest and Wallace in the American South) meant they had scant chance of winning a national election.