The 1864 election was the first time since 1812 that a presidential election took place during a war.

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 Cold Harbor, the Battle of Brices Cross Roads, the Battle of Kennesaw Mountain and the Battle of the Crater.
In addition, the war was continuing to take a very high toll in terms of casualties with campaigns such as Grant's Overland Campaign and the perceived lack of progress.
The prospect of a long and bloody war started to make the idea of "peace at all cost" offered by the Copperheads look more desirable.
Because of this, McClellan was thought to be a heavy favorite to win the election.
Unfortunately for Lincoln, Frémont's campaign got off to a good start.

However, several political and military events eventually made Lincoln's re-election inevitable.
In the first place, the Democrats had to confront the severe internal strains within their party at the Democratic National Convention.
The political compromises made at the Democratic National Convention were contradictory and made McClellan's efforts to campaign seem inconsistent.

Secondly, the Democratic National Convention influenced Frémont's campaign.
Frémont was appalled at the Democratic platform, which he described as "union with slavery".
After three weeks of discussions with Cochrane and his supporters, 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.
General Cochrane, who was a War Democrat, agreed and withdrew with Frémont.
On September 23, 1864 Frémont also brokered a political deal in which Lincoln removed U.S. Postmaster General Montgomery Blair from office, and on September 24 Abraham Lincoln relieved Blair of his duty as Postmaster General.
McClellan's chances of victory faded after Frémont withdrew from the presidential race.

Lastly, with the fall of Atlanta on September 2, there was no longer any question that a Union military victory was inevitable and close at hand.

In the end, the Union Party mobilized the full strength of both the Republicans and the War Democrats under the slogan "Don't change horses in the middle of a stream".
It was energized as Lincoln made emancipation the central issue, and state Republican parties stressed the perfidy of the Copperheads.
The 1864 election was the first time since 1812 that a presidential election took place during a war.
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 Cold Harbor, the Battle of Brices Cross Roads, the Battle of Kennesaw Mountain and the Battle of the Crater. In addition, the war was continuing to take a very high toll in terms of casualties with campaigns such as Grant's Overland Campaign and the perceived lack of progress. The prospect of a long and bloody war started to make the idea of "peace at all cost" offered by the Copperheads look more desirable. Because of this, McClellan was thought to be a heavy favorite to win the election. Unfortunately for Lincoln, Frémont's campaign got off to a good start.
However, several political and military events eventually made Lincoln's re-election inevitable. In the first place, the Democrats had to confront the severe internal strains within their party at the Democratic National Convention. The political compromises made at the Democratic National Convention were contradictory and made McClellan's efforts to campaign seem inconsistent.
Secondly, the Democratic National Convention influenced Frémont's campaign. Frémont was appalled at the Democratic platform, which he described as "union with slavery". After three weeks of discussions with Cochrane and his supporters, 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. General Cochrane, who was a War Democrat, agreed and withdrew with Frémont. On September 23, 1864 Frémont also brokered a political deal in which Lincoln removed U.S. Postmaster General Montgomery Blair from office, and on September 24 Abraham Lincoln relieved Blair of his duty as Postmaster General. McClellan's chances of victory faded after Frémont withdrew from the presidential race.
Lastly, with the fall of Atlanta on September 2, there was no longer any question that a Union military victory was inevitable and close at hand.
In the end, the Union Party mobilized the full strength of both the Republicans and the War Democrats under the slogan "Don't change horses in the middle of a stream". It was energized as Lincoln made emancipation the central issue, and state Republican parties stressed the perfidy of the Copperheads.
1864 United States presidential election