Southern sympathizers in the North were referred to as “doughfaces”. Despite being an etymology fan, I’d never thought to research the word’s origin ’til now. It’s pretty great. Here’s the short answer:
The term doughface originally referred to an actual mask made of dough, but came to be used in a disparaging context for someone, especially a politician, who is perceived to be pliable and moldable.
There’s a full history of the word that’s worth a read at the link below.