Lyman Trumbull in the context of "United States Senate Committee on the Judiciary"

Moderate Republicans were a faction of American politicians within the Republican Party from the party's founding before the American Civil War in 1854 until the end of Reconstruction in the Compromise of 1877. They were known for their loyal support of President Abraham Lincoln's war policies and opposed the more militant stances advocated by the Radical Republicans. According to historian Eric Foner, congressional leaders of the faction were James G. Blaine, John A. Bingham, William P. Fessenden, Lyman Trumbull, and John Sherman. Their constituencies were primarily residents of states outside New England, where Radical Republicanism garnered insufficient support. They included "Conservative Republicans" and the moderate Liberal Republicans, later also known as "Half-Breeds".

During the 1864 United States presidential election, amidst the backdrop of the ongoing Civil War, moderate Republicans supported merging the Republican Party with the War Democrats (Democrats who supported the continuation of the Union war effort) to form the National Union Party alliance. At the Republican National Convention (which operated under the name of the "National Union National Convention" that year), they spearheaded the effort to replace Lincoln's vice president Hannibal Hamlin with Tennessee Democrat Andrew Johnson, acting out of the belief that placing a War Democrat on the presidential ticket would solidify support to ensure Lincoln's re-election.

The Liberal Republican Party was an American political party that was organized in May 1872 to oppose the reelection of President Ulysses S. Grant and his Radical Republican supporters in the presidential election of 1872. The party emerged in Missouri under the leadership of Senator Carl Schurz and soon attracted other opponents of Grant; Liberal Republicans decried the scandals of the Grant administration and sought civil service reform. The party opposed Grant's Reconstruction policies, particularly the Enforcement Acts. It lost in a landslide, and disappeared from the national stage after the 1872 election.

The Republican Party had emerged as the dominant party in the aftermath of the Civil War, but many original Republicans became dissatisfied with the leadership of President Grant. Prominent liberal leaders like Schurz and Lyman Trumbull had been leaders in the fight against slavery and for the first stages of Reconstruction. They considered the task accomplished, and thought continued radical policies to be oppressive. By 1872, they demanded an end to Reconstruction and a restoration of self-government to the South.