For much of 1864, Lincoln himself believed he had little chance of being re-elected. Confederate forces had triumphed at the Battle of Mansfield, the Battle of the Crater, and the Battle of Cold Harbor and the war was continuing to take a very high toll in terms of casualties. During three months in the summer of 1864, over 65,000 Union soldiers were killed, wounded, or missing-in-action. In comparison, there had been 108,000 Union casualties in the first three years. The prospect of a long and bloody war started to make the idea of "peace at all cost" offered by the Democrats look more appealing.
On August 23, Lincoln wrote the following: “This morning, as for some days past, it seems exceedingly probable that this Administration will not be re-elected. Then it will be my duty to so co-operate with the President-elect as to save the Union between the election and the inauguration; as he will have secured his election on such ground that he can not possibly save it afterwards.” Lincoln folded the note, sealed it, and asked the members of his Cabinet to sign the back of the paper without reading it. They did so.
As it will this year, the presidential election of 1864 was held on November 8th. In order to appeal to those who supported the war, the Democrats nominated General George B. McClellan as their candidate. Like the Republicans, the Democratic Party was also split between War Democrats and Peace Democrats. Moderate Democrats supported the war against the Confederacy, but they were now calling for a negotiated peace. Radical Peace Democrats known as Copperheads believed that the war was a failure. They favored an immediate end to the war. McClellan was seen as a strong candidate who could unify the party. The pro-war McClellan was selected as the party's candidate for president and anti-war Representative George H. Pendleton was selected as the party's candidate for vice-president.
An event known as the Radical Democracy Convention was held on May 29, 1864. General John C. Frémont, who had been the first presidential candidate for the Republican Party in 1856, was selected as their candidate. But Frémont withdrew from the race in September 1864. In his statement, Frémont declared that winning the Civil War was too important to divide the Republican vote. Although he still felt that Lincoln was not going far enough, the defeat of McClellan was of the greatest necessity. Frémont also brokered a political deal with Lincoln in which Lincoln removed Postmaster General Montgomery Blair from office.
Perhaps the thing that saved Lincoln's bid for re-election most was the fall of Atlanta on September 2. It turned out to be a September surprise, rather than an October surprise, but in those days news traveled a lot slower than it does today. On August 31, General William Tecumseh Sherman's army captured the railroad track from Macon top Atlanta. With his supply lines fully severed, Confederate General John Bell Hood pulled his troops out of Atlanta the next day, September 1, destroying supply depots as he left to prevent them from falling into Union hands. He also set fire to eighty-one loaded ammunition cars, which led to a conflagration watched by hundreds. The next day, on September 2, Mayor James Calhoun, along with a committee of leading formally surrendered the city. Sherman sent a telegram to Washington on September 3, reading, "Atlanta is ours, and fairly won". He then established his headquarters there on September 7, where he stayed for over two months. On November 15, the army departed east toward Savannah for what became known as "Sherman's March to the Sea".
The fall of Atlanta and the overall success of this military campaign were extensively covered by Northern newspapers, and were a boon to Northern morale and to President Lincoln's political standing. Suddenly the Democratic Party's call for negotiations with the Confederacy on the subject of a potential truce was not as popular. The capture of Atlanta and Hood's burning of military facilities as he evacuated showed that a successful conclusion of the war was in sight, weakening support for a truce. Republicans, under the banner of the National Union Party, campaigned on the slogan "Don't change horses in the middle of a stream." Many war Democrats joined them.
Only 25 states participated in the election, since 11 Southern states had declared secession from the Union. Three new states participated in a presidential election for the first time: Kansas, West Virginia, and Nevada. The reconstructed portions of Tennessee and Louisiana chose presidential electors, although Congress did not count their votes. Just for added measure, Lincoln arranged for leave for Union soldiers in those states where they were required to be physically present in the state to vote on election day. Lincoln received 2,218,388 votes (55.0%) and 212 electoral votes. McClellan received 1,812,807 votes (45.0%) and 21 electoral votes. McClellan won just three states: Kentucky, Delaware, and his home state of New Jersey. Lincoln won in every state he carried in 1860 except New Jersey, and also carried a state won four years earlier by Stephen Douglas (Missouri), one carried by John C. Breckenridge (Maryland) and all three newly admitted states (Kansas, Nevada and West Virginia). Soldiers were allowed to vote in the field if they came from the following states: California, Kansas, Kentucky, Maine, Michigan, Rhode Island, and Wisconsin. Out of the 40,247 army votes cast, Lincoln received 30,503 (75.8%) and McClellan 9,201 (22.9%).