During the American Civil War (1861-1865), the Copperheads nominally favored the Union and strongly opposed the war, for which they blamed abolitionists, and they demanded immediate peace and resisted draft laws. They wanted Lincoln and the Republicans ousted from power, seeing the president as a tyrant who was destroying American republican values with his despotic and arbitrary actions.
Some Copperheads tried to persuade Union soldiers to desert. They talked of helping Confederate prisoners of war seize their camps and escape. They sometimes met with Confederate agents and took money. The Confederacy encouraged their activities whenever possible. Most Democratic party leaders, however, repelled Confederate advances.
John Mullaly's Metropolitan Record was the official Catholic paper in New York City. Reflecting Irish opinion, it supported the war until 1863 before becoming a Copperhead organ; the editor was then arrested for draft resistance. Even in an era of extremely partisan journalism, Copperhead newspapers were remarkable for their angry rhetoric. "A large majority [of Copperheads]," declared an Ohio editor, "can see no reason why they should be shot for the benefit of niggers and Abolitionists." If "the despot Lincoln" tried to ram abolition and conscription down the throats of white men, "he would meet with the fate he deserves: hung, shot, or burned. Through the 1864 election, Wisconsin newspaper editor Marcus M. Pomeroy called Lincoln "fungus from the corrupt womb of bigotry and fanaticism" and a "worse tyrant and more inhuman butcher than has existed since the days of Nero... The man who votes for Lincoln now is a traitor and murderer... And if he is elected to misgovern for another four years, we trust some bold hand will pierce his heart with dagger point for the public good."
Probably the largest Copperhead group was the Knights of the Golden Circle; formed in Ohio in the 1850s, it became politicized in 1861. It reorganized as the Order of American Knights in 1863, and again, early in 1864, as the Order of the Sons of Liberty, with Vallandigham as its commander. One leader, Harrison H. Dodd, advocated violent overthrow of the governments of Indiana, Illinois, Kentucky, and Missouri in 1864. Democratic party leaders, and a Federal investigation, thwarted his conspiracy. In spite of this Copperhead setback, tensions remained high. The Charleston Riot took place in Illinois in March 1864. Indiana Republicans then used the sensational revelation of an antiwar Copperhead conspiracy by elements of the Sons of Liberty to discredit Democrats in the 1864 House elections. The military trial of Lambdin P. Milligan and other Sons of Liberty revealed plans to set free the Confederate prisoners held in the state. The culprits were sentenced to hang but the Supreme Court intervened in Ex parte Milligan, saying they should have received civilian trials.
Most Copperheads actively participated in politics. On May 1, 1863, former Congressman Vallandigham declared that the war was being fought not to save the Union but to free the blacks and enslave Southern whites. The Army then arrested him for declaring sympathy for the enemy. He was court-martialed and sentenced to imprisonment, but Lincoln commuted the sentence to banishment behind Confederate lines. The Democrats nevertheless nominated him for governor of Ohio in 1863; he campaigned from Canada but was defeated after an intense battle. He operated behind-the-scenes at the 1864 Democratic convention in Chicago; this convention adopted a largely Copperhead platform, but chose a pro-war presidential candidate, George B. McClellan. The contradiction severely weakened the chances to defeat Lincoln's reelection.
There was an earthy quality in Voorhees, "the tall sycamore of the Wabash." On the stump his hot temper, passionate partisanship, and stirring eloquence made an irresistible appeal to the western Democracy. His bitter cries against protective tariffs and national banks, his intense race prejudice, his suspicion of the eastern Yankee, his devotion to personal liberty, his defense of the Constitution and State's rights faithfully reflected the views of his constituents. Like other Jacksonian agrarians, he resented the political and economic revolution then in progress. Voorhees idealized a way of life which he thought was being destroyed by the current rulers of his country. His bold protests against these dangerous trends made him the idol of the Democracy of the Wabash Valley. [Stampp, p. 211]