1862–63 United States Senate elections

The 1862–63 United States Senate elections were held from January 4, 1862, to November 13, 1863. Regularly scheduled elections were held for 20 out of the 70 seats in the United States Senate, and special elections were held in Indiana, Illinois, Michigan, Missouri, New Jersey, Oregon, and Rhode Island. The Republican-Union coalition kept the majority they had held since 1861 despite an unfavorable national environment.

U.S. senators are divided into three classes whose six-year terms are staggered, such that one-third of the Senate is elected every two years. Senators in Class 1 were elected in 1862 and 1863. Prior to ratification of the Seventeenth Amendment, senators were elected by the U.S. state legislatures. There was no fixed calendar, and states held elections on various dates preceding the first session of Congress. In states with split partisan control of the legislature, multiple rounds of voting could be required to elect a senator, leading to extended vacancies.

The elections took place against the backdrop of civil war and emancipation in what was the first real test of Democratic opposition to the Lincoln administration. The war disrupted established party systems in the free states and the loyal border states, resulting in a partial political realignment. In the Lower North, Republicans and War Democrats contested these elections as the Union Party, while Republicans maintained a separate organization in New England and the Upper Midwest. In Massachusetts and Rhode Island, conservative opponents of the Republicans formed new political parties composed of most Democrats and Constitutional Unionists. In the border states, Unionists were ascendant but internally divided over issues relating to slavery and Reconstruction, resulting in protracted legislative battles in Missouri and West Virginia.

Emancipation and the status of freedpeople were major issues during the campaign and a significant factor in party alignments. Lincoln's initial plan of gradual, compensated emancipation paired with the colonization of freedpeople outside the United States was jointly rejected by abolitionists who favored immediate, unqualified emancipation, and by Democrats and conservatives who opposed emancipation altogether. Radical Republican opposition to any compromise with slavery was the catalyst for the formation of the People's Party in Massachusetts, who campaigned in support of Lincoln's proposal. The manner and timing of emancipation split the Missouri unionist movement, leading radical Immediate Emancipationists to organize the Radical Union Party in September 1863. The appearance of the preliminary Emancipation Proclamation in September 1862 interrupted the campaign and undercut the momentum of pro-Lincoln conservatives. Democrats attempted to capitalize on racist backlash to the proclamation, warning that emancipation would precipitate slave rebellions and large-scale Black migration to the free states, and charging the administration of prolonging the war in service of religious fanaticism. While Radical Republicans celebrated the proclamation, Moderates and Conservatives feared the president's policy spelled electoral defeat. In Ohio, Republican-Unionists avoided mention of slavery in their state platform, and the Indiana Union Party called for the restoration of the Union with the rights of the states fully intact.

While Democrats made significant gains in the concurrent elections for the House of Representatives and won important state races in Illinois, Indiana, and New York, the party failed to improve its standing in the Senate and instead suffered a net loss of seats. Republican-Unionists flipped Democratic-held seats in California, Oregon, and Minnesota, while Democrats flipped Republican-held seats in Illinois and Pennsylvania. In Indiana and New Jersey, Democrats defeated Republican-Union incumbents appointed to fill vacancies caused by the expulsion or death of a Democratic senator less than a year before the election. Radical Unionists gained both Missouri seats held by Democrats prior to 1862, and Constitutional Unionists flipped a Republican-held seat in Rhode Island. No election was held in Tennessee following the resignation of Democrat Andrew Johnson, increasing the number of vacancies to 20.

The death of James A. Pearce of Maryland reduced the Democratic caucus to nine seats before the start of the 38th Congress. The Missouri Radical Unionists, both Union senators from West Virginia, and Constitutional Unionist William Sprague of Rhode Island subsequently caucused with the Republican-Union majority, increasing their caucus to 36 seats.