President Lincoln did not comment on the Thirteenth Amendment during early congressional debates and in the weeks immediately following passage by the Senate, although he was working behind the scenes to see that Arkansas, Louisiana, and Tennessee (all under Union control) enacted antislavery constitutions during the Reconstruction process.  Prior to General William Sherman’s victory in Atlanta in September 1864, Lincoln faced criticism of the Union military’s failure to secure victory in the war and of his administration’s policies, particularly on emancipation and the military draft.  Opposition within the Republican Party came from a group of radicals who argued that Lincoln’s commitment to emancipation and the use of black troops was too limited and that his Reconstruction plan was too mild and cautious.  They decided that the party required new leadership and began looking for an alternative candidate to run for president.  General Benjamin Butler, General Ulysses S. Grant, and Treasury Secretary Salmon P. Chase all declined to challenge the president (Chase after a trial balloon failed to launch). 

On May 31, 1864, an unusual political alliance of abolitionists, Missouri radicals, anti-Lincoln German-Americans, and New York War Democrats met at a national convention in Cincinnati under the party label of the Radical Democracy.  Delegates nominated for president John C. Fremont, the Republican Party’s first presidential nominee in 1856 and the Union General whose emancipation proclamation for Missouri had been rescinded by President Lincoln in September 1861.  To balance the ticket, the vice-presidential nomination went to John Cochrane, a War Democrat and former congressman from New York.  Among other measures, the platform of the Radical Democracy endorsed the Thirteenth Amendment to abolish slavery as well as a constitutional amendment to protect civil rights (later incorporated in the Fourteenth Amendment).   

A cartoon in the July 2, 1864 issue of Harper’s Weekly depicted Fremont as a boy holding a black doll, which symbolized the Radical Democracy’s support of abolition and black civil rights.  In the cartoon, Miss Columbia wonders whether Fremont’s candidacy is due to insanity.  Brother Jonathan (a prototype of Uncle Sam) appears as a physician who reassuringly diagnoses it as due to resentment over Lincoln’s treatment in rescinding the Missouri emancipation order, as well as twice relieving Fremont of his military command.  It was common for the press to refer to dissident radical Republicans as “soreheads.”

According to historian Michael Vorenberg, it was the Radical Democracy’s embrace of the Thirteenth Amendment that prompted Lincoln to ensure that the platform of the Republican Party endorsed the measure in order to undermine criticism of his administration.  The president convinced Senator Edwin Morgan of New York, chairman of the Republican National Committee, to make the Thirteenth Amendment the centerpiece of Morgan’s opening address at the national convention.  Republicans met in Baltimore on June 7-8, 1864, under the National Union banner in order to attract support from War Democrats.  Delegates ratified a platform calling for an abolition amendment, without mentioning the Senate-approved Thirteenth Amendment specifically.  

After the National Union Convention, the Thirteenth Amendment became more exclusively associated with the Republican Party.  The changed political landscape was evident during the highly partisan debate in the U.S. House, where on June 15, 1864, the proposed Thirteenth Amendment fell 11 votes short of the needed two-thirds majority needed for passage.   

In the July 23 issue of Harper’s Weekly, editor Curtis explained how the Lincoln administration had overseen numerous federal acts that undermined the institution of slavery and advanced civil rights for black Americans.  He then argued how Fremont’s candidacy and its criticism of Lincoln were playing into the hands of Peace Democrats like Clement Vallandigham whose proposed policy of a negotiated settlement with the Confederacy would leave slavery as a legal institution.   

The Democratic National Convention, meeting in Chicago on August 29-30, 1864, was indeed dominated by Vallandigham, Fernando Wood, and other Peace Democrats.  As expected, the national party platform endorsed a cease-fire and negotiated settlement with the Confederacy.  Delegates nominated Union General George B. McClellan for president and Congressman George Pendleton, a Peace Democrat, for vice president.  McClellan, however, was a War Democrat who distanced himself from the peace plank of his party’s platform and vowed to administer the Union war effort more effectively than Lincoln.   

Nevertheless, Republican cartoonists targeted the “Chicago Platform,” most memorably by Thomas Nast in the October 15, 1864 issue of Harper’s Weekly.  The intricate double-page illustration interweaves twenty pictures with extracts from the Democratic platform, McClellan’s letter of acceptance, and a Pendleton speech.  The center image of McClellan reminds voters of the Union general’s failed expedition to capture the Confederate capital of Richmond.  That scene is surrounded by images of anti-Union and anti-black violence and humiliation perpetrated by Confederates and their Northern sympathizers.  The vignettes attempted to show in pictures what the words of the Democratic platform and speeches really meant when put into action.  In the circular illustration on the far right of the center panel, for example, the platform call for “rights of the states unimpaired” allows slaves to be whipped mercilessly by their masters.  In the circular illustration on the far left of the center panel “the constitution itself has been disregarded” shows that the words refer to the Emancipation Proclamation.  Nast’s “Chicago Platform” was printed and widely distributed as a Lincoln campaign poster. 

In early September 1864, General William T. Sherman’s capture of Atlanta revived Union military prospects and the chances for Lincoln’s reelection.  Fremont’s candidacy failed to gain momentum, and he withdrew from the race in late September.  On November 8, 1864, Lincoln defeated McClellan in the Electoral College, 212-21, and Republicans gained seats in Congress, giving them unassailable control, 149 to 42 in the House and 42 to 10 in the Senate.  Republicans had hoped to make the Thirteenth Amendment the main issue in the campaign, but the military situation and Democratic race baiting dominated the national debate, as the draft and Union loyalty did at the state level.