Regan democrats were conservative democrats, sort of like what we used to call Scoop Jackson democrats. A primary characteristic is strong on national defense.
This is one fairly good description of “middle”.
Another is to remove the far right wing and far left wing and what you have left is... the middle.
"Strong on national defense" can cover a multitude of positions. SDI? 500-ship Navy? Pre-emptive strikes?
How strong does it have to be before you've gone over the edge and become an aggressor?
Sorry, I'm not buying defense as a defining element of moderation or even conservatism. It covers too much ground.
Got to go for now, but I'd welcome other ideas at a later time. Good night.