Why Romney? Well, it may have something to do with the fact that Idaho is second only to Utah in number of Mormon residents. A full 24 percent of its population belongs to The Church of Jesus Christ of Latter-Day Saints, according to a Gallup study out last month.
In the ad, Romney touts Simpson as "the conservative choice" and says: "Mike is fighting hard every day to cut Washington's wasteful spending, to stop junk lawsuits and to fight against Obamacare."
Simpson is running in a tight primary against Bryan Smith, a lawyer backed by the Club for Growth and other groups associated with the Tea Party movement who don't view him a good on cutting spending. Simpson's congressional voting record earned him a 57 percent lifetime rating from the Club.