Republican presidential candidates (L-R) U.S. Rep. Ron Paul (R-TX), former U.S. Sen. Rick Santorum, former Massachusetts Gov. Mitt Romney and former Speaker of the House Newt Gingrich participate in a debate sponsored by CNN and the Republican Party of Arizona at the Mesa Arts Center February 22, 2012 in Mesa, Arizona. The debate is the last one scheduled before voters head to the polls in Michigan and Arizona's primaries on February 28 and Super Tuesday on March 6.