Would "neo-Copperhead" be an improvement in terminology? More people have read about the Copperheads than about Vallandigham in particular, or where he diverged from Lincoln.
Of course, the term "Copperhead" is itself prejudicial (he said, raising a difficulty to his own proposal), and some people like Vallandigham and Navy Secretary Gideon Welles (who agreed with Vallandigham about habeas corpus and the closing of Democratic newspapers, but kept his mouth shut and did as he was told) were principled moderates who perhaps had reservations about Lincoln's policies; but if they said anything publicly like Vallandigham, they were systematically stigmatized and, in Vallandigham's case, actually jailed for expressions of view on the peremptory order of General Ambrose Burnside and a military trial court.
Since we are all using Vallandigham's name, it might be useful to recall that he was a moderate Democrat who supported Douglas against Breckinridge and the bolters in 1860, who personally opposed slavery, and whose opposition to Lincoln was principled rather than gratuitous, and founded in constitutional law, about which he was passionate and even quarrelsome. Of course, nobody is quarrelsome about con law any more.
Perhaps it would be helpful or enlightening if you could compare and contrast for us the terms "Constitutionalist" and "Declarationist"?
Regards,
Amelia
(who thinks she has a general idea but would like to be sure)