WASHINGTON (AP) - The head of the Republican Governors Association says Rick Santorum's withdrawal from the presidential sweepstakes should signal party conservatives to unify behind Mitt Romney.

Virginia Gov. Bob McDonnell tells "CBS This Morning" that "conservatives, independents and clear-thinking moderates are now going to get behind" the former Massachusetts governor.

He says he believes Republicans have an excellent chance to make Barack Obama a one-term president, and that party people should be "keeping their eyes on the big prize, which is winning the presidency." McDonnell says he believes Santorum "can bring a lot of people in" to the cause.

McDonnell, whose name has surfaced in speculation about the vice presidential nomination, tells the network "ultimately, that's up to the nominee. I'm perfectly happy being the governor of Virginia."