Former Massachusetts Gov. Mitt Romney waves to the crowd as he is introduced at the start of Wednesday night's Republican presidential debate in Mesa, Ariz. Ross D. Franklin/AP hide caption

itoggle caption Ross D. Franklin/AP

Republican presidential hopeful and former U.S. Sen. Rick Santorum speaks to supporters, flanked by his daughter, Elizabeth (left), and wife, Karen. Whitney Curtis/Getty Images hide caption

itoggle caption Whitney Curtis/Getty Images

Rep. Michele Bachmann waves to supporters Friday in Sioux City before starting a 99-county bus tour of Iowa. Jeff Haynes/Reuters /Landov hide caption

itoggle caption Jeff Haynes/Reuters /Landov