“That the attack wasn’t too bright goes without saying — it was a Democratic Party idea.”
The man who ordered the firing on Ft Sumter, General PGT Beauregard, had run for mayor of New Orleans in 1858. He was promoted by both the Whig and the Democratic Parties. The Whigs were Lincoln’s old party.
There may have been a rump who didn't go over to the Democrats or the American (Know Nothing) Party, and they would have been the ones to endorse PGTB, the Democratic candidate.
Beauregard was a lifelong Democrat according to one source.