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: