[97] He reluctantly supported efforts to enlist former slaves into the Union Army, feeling that African-Americans should perform menial tasks to release white Americans to do the fighting.[98] Nevertheless, he succeeded in recruiting 20,000 black soldiers to serve the Union.[99]

Vice presidency (1865)
Main article: 1864 United States presidential election
Poster for the Lincoln and Johnson ticket by Currier and Ives
In 1860, Lincoln's running mate had been Senator Hannibal Hamlin of Maine. Although Hamlin had served competently, was in good health, and was willing to run again, Johnson emerged as running mate for Lincoln's reelection bid in 1864.[100]
Lincoln considered several War Democrats for the ticket in 1864, and sent an agent to sound out General Benjamin Butler as a possible running mate. In May 1864, the president dispatched General Daniel Sickles to Nashville on a fact-finding mission. Although Sickles denied that he was there either to investigate or interview the military governor, Johnson biographer Hans L. Trefousse believes that Sickles's trip was connected to Johnson's subsequent nomination for vice president.[100] According to historian Albert Castel in his account of Johnson's presidency, Lincoln was impressed by Johnson's administration of Tennessee.