William Jennings Bryan resigned before American Entry into World War I, right after the sinking of the Lusitania. He was troubled by Wilson's refusal to advise Americans that as citizens of a neutral nation they traveled on belligerent ships at their own risk. Additionally, his advice to urge the acceptance of German proposals for a relaxation of submarine warfare in return for relaxation of the British food blockade against Germany was ignored. "Why be shocked at the drowning of a few people, if there is no objection to starving a nation?" he asked. (Source: American Political Tradition, Richard Hofstadter, pp. 260-261)

William Jennings Bryan never ran as a Populist. He ran as a democrat, the 'fusionists' in the Populist Party managed to secure his endorsement by also nominating him. Bryan never took up the populist platform, saying simply that there were some planks of the Populist Party of which he did not approve, never mentioning specifics.