For the purpose of the 1864 election, the Republican Party went under the rubric National Union Party, the better to attract War Democrats. The nominating convention was in Baltimore, and Lincoln had that part of the contest fairly much sewn up. In May, a small splinter of the Republican Party had nominated John C. Fremont, the explorer and 1856 Republican standard-bearer, for president at a "Peoples Convention" in Cleveland. Little was to come of it.
According to Larry T. Balsamo, writing in the Journal of the Illinois State Historical Society in the Summer 2001 issue: "At about the time of the Cleveland Convention, John Hay in conversation with Lincoln noted that [John C.] Fremont could be a dangerous adversary if he achieved military and political influence, but that he seemed to lack energy and ability. According to Hay's diary Lincoln remarked, 'Yes, he is like Jim Jett's brother. Jim used to say that his brother was the damnedest scoundrel that ever lived, but in the infinite mercy of Providence he was also the damnedest fool.'
"The convention of the National Union Party in early June of 1864 was unusually placid and orderly. With his adroit and sometimes ironhanded use of the patronage, the demise of the Chase candidacy, and with Fremont and his supporters essentially out of the party, Lincoln's renomination was accomplished on the initial ballot with only the stubborn Missouri delegation opposed. The platform, including support for a constitutional amendment to end slavery, support for completion of the transcontinental railroad, and a specific endorsement of the policies of the Lincoln administration, was adopted almost without debate.
"The only real surprise and occasion for future historical controversy was the selection of Andrew Johnson to replace the incumbent Hannibal Hamlin as the Vice Presidential nominee. It now appears that Lincoln did not engineer this change, but he certainly did not oppose it. Lincoln's secretary John G. Nicolay was overseeing the president's interests at the Baltimore Convention and he wrote to John Hay in Washington on the first day of the convention seeking instructions. One of Lincoln's Illinois friends, Norman Judd, was gathering support for Joseph Holt, the Judge Advocate General of the U.S. Army and a Kentuckian, for the second spot on the ticket. On Nicolay's letter sent through Hay, Lincoln wrote 'Mr. Holt is a good man, but I have not heard or thought of him for VP. Wish not to interfere about VP. Can not interfere about platform. Convention must judge for itself.' "