Actually there is one Blue State with the Mason-Dixon in it, MD. Those of us unfortunate enough to reside here want to change the state slogan from “Free State” to “Freedomless State”. It is personal opinion the Mason-Dixon is a state of mind but actually runs slightly above Fredericksburg, VA.
and as far north as the southern suburbs of Bloomington, Indiana.
I've never considered Maryland to be part of the Confederacy below the Mason-Dixon line back in those days; nor the Northern portions of Virginia.
Admittedly, I'm just spouting without doing further research. ....My opinion is probably driven by the liberalism that exists in those areas.