Questions: Which candidate's scandal-filled presidency prompted Teddy Roosevelt to run in the 1912 presidential election?

The answer is William Taft.

Franklin Roosevelt was not involved in the 1912 presidential election. He served as the 32nd President of the United States from 1933 to 1945, long after the events of 1912.

William Taft was the 27th President of the United States, serving from 1909 to 1913. His presidency was marked by a number of controversies and a perceived departure from the progressive policies of his predecessor, Theodore Roosevelt. Disappointed with Taft's performance and policies, Roosevelt decided to run against him in the 1912 election, leading to a split in the Republican Party.

Woodrow Wilson was the Democratic candidate in the 1912 election and eventually won the presidency. He was not the reason for Roosevelt's decision to run; rather, it was Taft's presidency that prompted Roosevelt to enter the race.