Copperheads, or Peace Democrats

The Copperheads were a faction of Democrats in the North who opposed the American Civil War. They were also called Peace Democrats (most of this summary is directly from Wikipedia)

Copperheads nominally favored the Union but they strongly opposed the war, for which they blamed abolitionists, and they demanded immediate peace and resisted the 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 their money. The Confederacy encouraged their activities whenever possible, and at one point Confederate agents controlled portions of the Democratic party in states such as Connecticut.
The Copperhead rhetoric in their press was red-hot in displaying their hatreds and bitterness. "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."

The McPherson book I have been mentioning lately For Cause and Comrades, has an interesting chapter on the effect of the Copperheads on the morale of the Union troops. All quotes are from that chapter, which in turn draws all its information from the letters and diaries of soldiers.

Democratic gains in the congressional and state elections in 1862 fell like a wet blanket on the army. The troops were “not in as good spirits and as cheerful as they were before the elections… The election of men whose antecedents prove them to be at least sympathizers with the South… it is a common saying here that if we are whipped, it will be by Northern votes, not by Southern bullets.”

The Peace Democrats not only discouraged the boys in blue but also encouraged the enemy “The Rebels in the South well know how we are divided in the North. It encourages them to hold out…”

“You can’t imagine how much harm these traitors are doing.” “I shall never want to see any of my relations that worked against me while I was in the service.” “Every copperhead, peaceman, anti-draft man, every cursed mother’s son of them that does not support the war by word and deed ought to be hung or sent to the south where they belong. There is no middle ground. Every man who is not for us is against us.”