What transformed U.S. politics in the 1920s was A. the return of the Republican Old Guard. In the election of 1920, the Democratic candidate strongly supported the League of Nations. On the other hand, the Republican candidate Warren Harding opposed it. His slogan was "a return to normalcy" which meant a return to the conditions before the war. He wanted to return to isolationism, and not to care for foreign problems. He won the election.
