re: "UK politics occupy about a 1 inch span slightly left of centre of the US 5 mile wide stretch "
"Do you feel much American political debate (as you see it here) is primarily an attempt to re-define just what a moderate or a centrist is?"
Nope. Almost every iota of US political debate I've seen in this place has more in common with an argument between two religions rather than an actual discussion of issues, policy and common sense.
It achieves exactly nothing.