Democrats see Obama as a centrist. On defense issues, they even see him as fairly right wing. Republicans see Obama as very far to the left.
Republicans do not believe that they need to move very far into the center to beat Obama. They saw McCain as too centrist in 2008. They see Romney as too centrist for 2012. None the less, Romney is beginning to look like the best compromise Republican candidate for the general election next year.
If the Republicans go with Romney in 2012 and he is beaten by Obama, there will be no compromise Republican Presidential candidate in 2016. The Republican Presidential candidate in 2016 will be an anti intellectual, fundamentalist Christian, anti abortion, anti immigrant, anti Muslim, strongly nationalistic militarist, free market capitalist who demands both decreased taxes and a balanced budget.
Who knows. That might win the Presidency for them.