Robert E. Lee's seizure of Washington City delayed the convention in Baltimore, but when it finally took place it renominated President Abraham Lincoln and Vice President Hannibal Hamlin respectively. In response the Radical Republicans seceded (a word used by both the Richmond Dispatch and the northern papers) and put forward General John C. Frémont (who had attempted to free Missouri's slaves in 1861, only to be overruled by Lincoln) with Senator Andrew Johnson of Tennessee, who still adamantly refused to admit that his home state no longer accepted the authority of Washington D.C.
In no better condition than the Republicans, the Democrats had barely finished nominating Governor Horatio Seymour of New York and Clement Vallandigham of Ohio on Semptember 5. This mismatched ticket (Seymour tended to be a War Democrat, and Vallandigham was a Copperhead) illustrated just how confused the Democrats were. General George McClellan had announced he would run an independent campaign like Frémont, with Edward Everett as his running mate.
During late September, Frémont gave a series of fiery speeches that put Lincoln on the defensive. Some former Democrats, like Benjamin Butler, had one foot and a couple of toes in the Frémont camp. Others, Lincoln loyalists like Edwin M. Stanton, were sorry to see the path ahead so rocky. Other Republicans, like William Seward, were against Lincoln but still within the party. At this time, McClellan was calling for an invasion of the Canadas.
It took until November 19 to work out whether Lincoln or Seymour had won, but Seymour ultimately triumphed.
McClellan won tiny, conservative Delaware and his home state of New Jersey, while Frémont prevailed only in radical Kansas. New York, Ohio and Pennsylvania gave Seymour 80 of his 138 electoral votes, while Lincoln garnered 83, McClellan 10, and Frémont but 3. Out of 4,000,000 votes cast, Seymour led Lincoln by but 32,000 (Seymour/Vallandigham: 1,671,580; Lincoln/Hamlin:1,638,415; Frémont/Johnson:436,337; McClellan/Everett;287,749).
In OTL, the 1864 election saw Abraham Lincoln and his running mate Andrew Johnson defeat George McClellan and his running mate George Pendleton in an electoral landslide. The Lincoln-Johnson ticket carried 212 electoral votes from 22 states. In addition to this, the ticket also carried Louisiana and Tennessee's 17 electoral votes. However, since they had not been readmitted back to the Union, the Congress did not count their votes. The McClellan-Pendleton ticket only carried the states of Delaware, Kentucky, and New Jersey with 21 electoral votes.
The election is significant as the last election in which the Republican Party did not nominate a candidate; rather, in a successful attempt to court War Democrats away from McClellan was made when the Republicans endorsed the newly-created National Union Party, a temporary alliance of all political factions which believed in vigorously prosecuting the war to its conclusion. The National Union Party, with the Republican endorsement, nominated the incumbent Republican president Lincoln but jettisoned the incumbent Republican vice president, Hannibal Hamlin, in favor of Johnson, a Democrat.
McClellan's support within the Democratic Party was reduced to the Peace Democrats, who wanted a negotiated peace with the rebels. William Sherman's capture of the rebel stronghold of Atlanta gave the Union a major military victory heading into the most intense part of the campaign season, and this victory, which suggested to many Unionists that a final triumph over the Confederacy was at hand, greatly eroded support for McClellan's platform.
Supporters of Horatio Seymour lobbied hard for his nomination by the Democrats, but Seymour himself withdrew his name from consideration. He was the Democratic nominee in 1868, when he was defeated by Ulysses S. Grant.
John C. Frémont was disenchanted with Lincoln's refusal to use the Civil War as a means of dismantling slavery once and for all. He initially mounted a campaign as the nominee of the "Radical Democracy Party", a party made up primarily of Radical Republicans who wanted an end to slavery and to racial inequality. John Cochrane was his running mate. However, as the campaign progressed, Frémont realized that Lincoln's re-election was preferable to McClellan's victory, and withdrew.