Before the election, some War Democrats joined the Republicans to form the National Union Party.
With the outcome of the Civil War still in doubt, some political leaders, including Salmon P. Chase, Benjamin Wade, and Horace Greeley, opposed Lincoln's re-nomination on the grounds that he could not win.
Chase himself became the only candidate to contest Lincoln's re-nomination actively, but he withdrew in March when a slew of Republican officials, including some within the state of Ohio upon whom Chase's campaign depended, endorsed Lincoln for re-nomination.
Lincoln was still popular with most members of the Republican Party, and the National Union Party nominated him for a second term as president at their convention in Baltimore, Maryland, on June 7–8, 1864.
The party platform included these goals: "pursuit of the war, until the Confederacy surrendered unconditionally; a constitutional amendment for the abolition of slavery; aid to disabled Union veterans; continued European neutrality; enforcement of the Monroe Doctrine; encouragement of immigration; and construction of a transcontinental railroad."
It also praised the use of black troops and Lincoln's management of the war.

Andrew Johnson, the former senator from and current military governor of Tennessee, was named as Lincoln's vice presidential running-mate.
The choice of Andrew Johnson as Lincoln's running mate was a politically calculated move by the Republican Party to ensure the electoral votes of the border states.
Others who were considered for the nomination, at one point or another, were former Senator Daniel Dickinson, Major General Benjamin Butler, Major General William Rosecrans, Joseph Holt, and former Treasury Secretary and Senator John Dix.
Before the election, some War Democrats joined the Republicans to form the National Union Party. With the outcome of the Civil War still in doubt, some political leaders, including Salmon P. Chase, Benjamin Wade, and Horace Greeley, opposed Lincoln's re-nomination on the grounds that he could not win. Chase himself became the only candidate to contest Lincoln's re-nomination actively, but he withdrew in March when a slew of Republican officials, including some within the state of Ohio upon whom Chase's campaign depended, endorsed Lincoln for re-nomination. Lincoln was still popular with most members of the Republican Party, and the National Union Party nominated him for a second term as president at their convention in Baltimore, Maryland, on June 7–8, 1864. The party platform included these goals: "pursuit of the war, until the Confederacy surrendered unconditionally; a constitutional amendment for the abolition of slavery; aid to disabled Union veterans; continued European neutrality; enforcement of the Monroe Doctrine; encouragement of immigration; and construction of a transcontinental railroad." It also praised the use of black troops and Lincoln's management of the war.
Andrew Johnson, the former senator from and current military governor of Tennessee, was named as Lincoln's vice presidential running-mate. The choice of Andrew Johnson as Lincoln's running mate was a politically calculated move by the Republican Party to ensure the electoral votes of the border states. Others who were considered for the nomination, at one point or another, were former Senator Daniel Dickinson, Major General Benjamin Butler, Major General William Rosecrans, Joseph Holt, and former Treasury Secretary and Senator John Dix.
1864 United States presidential election