The reason he formed his own political party was that in February 1912, former President Theodore Roosevelt wanted to run for nomination as a Republican candidate. The dispute was severe. Across the party was William Howard Taft, Roosevelt's longtime friend who was running for re-election. The party machine was in the hands of Taft's followers. Roosevelt, knowing that he would be defeated, founded a new progressive party.
The new party became known as the Bull Moose Party.