[central_va]

They were sometimes hunted down, arrested & tried for treason.

BS, one of them ran as vice president with McClellan in '64. Copperheads were not hunted down at all. they were a viable political force in the North.

[rockrr]

Read your history. George H. Pendleton (McClellan's VP)wasn't a copperhead.

From Wackypedia:

The Copperheads sometimes talked of violent resistance, and in some cases started to organize. They never actually made an organized attack, however. As war opponents, Copperheads were suspected of disloyalty, and their leaders were sometimes arrested and held for months in military prisons without trial. One famous example was General Ambrose Burnside's 1863 General Order Number 38, issued in Ohio, which made it an offence (to be tried in military court) to criticize the war in any way.[8] The order was used to arrest Ohio congressman Clement L. Vallandigham when he criticized the order itself.[9] Lincoln, however, commuted his sentence while requiring his exile to the Confederacy.

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.[10]

[BroJoeK]

central_va: "BS, one of them ran as vice president with McClellan in '64. Copperheads were not hunted down at all.
they were a viable political force in the North."

I would not call Democrat McClellan a "copperhead", since even he denied wishing to make a compromise peace with the Confederacy.
Other Democrat-copperheads were not so reticent:

"The Copperheads were a vocal faction of Democrats located in the Northern United States of the Union who opposed the American Civil War, wanting an immediate peace settlement with the Confederates.
Republicans started calling antiwar Democrats "Copperheads", likening them to the venomous snake.
The Democrats accepted the label, reinterpreting the copper "head" as the likeness of Liberty, which they cut from Indian Head cents and proudly wore as badges.[1]
Democratic supporters of the war, by contrast, were called War Democrats."

[Copperheads] "...comprised the more extreme wing of the "Northern Democrats".
Two of the more famous Copperheads were Democratic congressmen from Ohio: Clement L. Vallandigham and Alexander Long.
Republican prosecutors accused some leaders of treason in a series of trials in 1864.[2]"

Copperhead pamphlet: