Final answer:
Theodore Roosevelt's decision to run for president in 1912 resulted in a split in the Republican Party, leading to the formation of the Progressive Party and ultimately aiding Democrat Woodrow Wilson's victory in the election. The correct option is C.
Step-by-step explanation:
Theodore Roosevelt's decision to run for president in 1912 as a Progressive, after failing to secure the Republican nomination, had a profound impact on the Republican Party. Roosevelt, feeling alienated by the conservative Republicans who renominated President William Howard Taft, formed the Progressive Party, commonly known as the Bull Moose Party.
This action heralded a significant split in the Republican Party, polarizing its members between conservative Republicans and Progressive Republicans. The division resulted in a weakened Republican base during the 1912 presidential election, allowing the Democrat candidate, Woodrow Wilson, to win the presidency.
Roosevelt’s choice to run as a third-party candidate broke from political tradition and led to a shift in party dynamics. His Bull Moose Party advocated for progressive reforms such as women's suffrage, workers' rights, and more direct democracy, drawing away support from the Republicans and thereby splitting their vote.
Despite Roosevelt's personal popularity and progressive agenda, the creation of the Progressive Party did not result in lasting success, and by 1916, many former members returned to the Republican fold.