Tonight's debate is the last one before some key primaries.
There's a Republican Presidential debate tonight - the first in almost a month - just days ahead of two important primaries.
Mitt Romney is fighting to win his home state while Rick Santorum is trying to turn his Michigan success into votes in Arizona.
Rick Santorum is the one to watch tonight. He's soared ahead nationally and in Michigan, but still trails Mitt Romney in Arizona, where tonight's debate is being held. "I always have and I will win the states that matter to win this election," said, Rick Santorum, (R) Presidential Candidate.
Santorum's now under attack in a new ad from Ron Paul. Focusing on social issues worked for Santorum. Now Mitt Romney's looking right -- meeting with the tea party tomorrow in Michigan, and hammering President Obama. "Unfortunately, perhaps because of the people the President hangs around with, and their agenda, their secular agenda, they have fought against religion." Mitt Romney/ (R) Presidential Candidate
At tonight's debate, Santorum will get more scrutiny because he's the new frontrunner, but so will Mitt Romney. "He's under the microscope, he's under pressure he needs to do well, he needs to re-establish a sense that he is the front runner in the race." Stu Rothenberg/ Political Analyst, "The Rothenberg Political Report"
Newt Gingrich, far behind in the polls, is trying to connect with voters by focusing on a hot-button issue, gas prices.
Romney and Santorum will campaign in Arizona today before tonight's debate there.
Tracie Potts, NBC News.