Fundamentals. From a broad sense, this is the core of the debate. You just read it, in the title, right above these words.
This is the major difference between people who associate themselves with the "left or right" "libertarian vs statist" "liberal or conservative" and last but not least, Democrat or Republican. Even, though that argument is a different story. :)
So, what is this? (keep in mind I’m not perfect).