McClellan sought and obtained the Democratic party's 1864 presidential nomination, but the convention was dominated by Peace Democrats, or Copperheads, who wrote a platform calling the war a failure and demanding an immediate armistice, with vague reference to a possible, though in reality highly unlikely, future restoration of the Union by peaceful negotiation. McClellan, in his letter accepting the nomination, tried unsuccessfully to distance himself from this extreme position, emphasizing his determination to continue the war until the Union was restored. The people, however, perceived McClellan and the Democrats, not without reason, as the party of peace and disunion. In the event, major Federal victories during the fall of 1864, particularly the capture of Atlanta, made a mockery of the Democratic platform and helped ensure McClellan's defeat by a landslide. Vote totals among soldiers were even more starkly against him, even in the Army of the Potomac that once idolized him.
On election day, before the results were known, McClellan wrote out his resignation from the army. He could live comfortably on the wealth produced by his stockholdings in the Ohio & Mississippi Railroad. Disgusted with the electoral decision of the American people, he left the country in January 1865 and traveled in Europe for three years.