[...] As was true of the Democratic party as a whole, the influence of Peace Democrats varied with the fortunes of war. When things were going badly for the Union on the battlefield, larger numbers of people were willing to entertain the notion of making peace with the Confederacy. When things were going well, Peace Democrats could more easily be dismissed as defeatists. But no matter how the war progressed, Peace Democrats constantly had to defend themselves against charges of disloyalty. Revelations that a few had ties with secret organizations such as the Knights of the Golden Circle helped smear the rest.

The most prominent Copperhead leader was Clement L. Valladigham of Ohio, who headed the secret antiwar organization known as the Sons of Liberty. At the Democratic convention of 1864, where the influence of Peace Democrats reached its high point, Vallandigham persuaded the party to adopt a platform branding the war a failure, and some extreme Copperheads plotted armed uprisings.

[...] With the conclusion of the war in 1865 the Peace Democrats were thoroughly discredited. Most Northerners believed, not without reason, that Peace Democrats had prolonged war by encouraging the South to continue fighting in the hope that the North would abandon the struggle.