A more significant threat to the Union came from so-called 'Peace Democrats,' known in the North as 'Copperheads' for their treacherous, stealthy attacks. Forming secret societies, including the 'Knights of the Golden Circle,' Copperheads forged links to the Confederacy. How far their activities went remains a matter of debate, but both Lincoln and Davis thought them significant. Copperheads propagandized Confederate success, recruited for the Rebel cause, and, in extreme situations, even stole supplies, destroyed bridges, and carried correspondence from southern leaders. Congress had passed the conspiracy act of July 31, 1861, and included anti-treason measures in the second confiscation act of July 17, 1862, but officials seldom invoked those laws. Usually, irate local grand juries would bring indictments, but after the accused sat behind bars for a few days, judges would quietly dismiss their cases and release them.

One of the most vocal and public of Lincoln's critics, Ohio Democrat Congressman Clement L. Valladigham, gave an anti-administration speech in 1863 in which he claimed the Republicans were fighting the war to free blacks and to enslave whites. General Ambrose Burnside, then in command of the Department of the Ohio, arrested him for 'declaring sympathies for the enemy.' Denied habeus corpus, Vallandigham went before a military commission, which sentenced him to close confinement for the end of the war. The matter severely embarrassed Lincoln, who feared 'thousands of Vallandighams,' and found an exquisite solution: he commuted Vallandigham's sentence, but banished him to the Confederacy he claimed to love. Exiled to the South, Vallandigham embarked on a remarkable journey, running the blockade, sailing to Windsor, Canada, and then, with the aid of a fake mustache and a pillow under his suit, sneaking back into the United States in time for the campaign of 1864, again to castigate Lincoln. The entire incident revealed much about the nature of both men—Vallandingham, determined but spiteful; Lincoln, possessing enough of a sense of humor to pack Vallandingham off to the Confederacy—and by that time no further actions were taken

1. Randall, Civil War and Reconstruction, 395.
2. Randall, Civil War and Reconstruction, 397.