How would you limit Romney? As president he is the head of the party....who would oppose his leftist platform? The Democrats will push him further to the left and the Republicans will pass what the president pushes...just look at free meds for the old folks bush passed or no child left behind.
How would you limit Rommney?
Thru the boneheads in Congress. By getting the right people in Cabinet. By getting the right advisors hired. Lots of ways.