The primary with the most delegates at stake comes this Tuesday.
Another win for Mitt Romney over the weekend as the candidates prepare for tomorrow's primary in Illinois. Illinois has more delegates at stake than any other state so far this year except Georgia, but there's an odd twist to how those delegates are awarded.
Illinois is a so-called "loophole" primary, which means there will be a popular vote - and a separate vote for delegates. And the popular vote doesn't determine who gets those delegates.
Illinois is the next big prize - President Obama's home state.
Tomorrow's Republican Primary will decide most of the state's 69 delegates. "If we're able to come out of Illinois with a huge or surprise win, I guarantee you, I guarantee you that we will win this nomination." said Rick Santorum, (R) Presidential Candidate.
It's an uphill battle for Santorum. He's not on the ballot in all Illinois districts, and Mitt Romney's got a clear lead in the latest polls, up by as much as nine points.
Plus, Romney is coming in with momentum. He won Puerto Rico's 20 delegates Sunday. "Those who don't think Latino voters will vote for Republicans need to look at Puerto Rico," proclaimed Mitt Romney (R) Presidential Candidate.
But Democrats question whether Romney can seal the deal. "Every time it looks like Mr. Romney has some momentum, he gets set back. He hasn't been able to make the sale to his own party," said Sr. Advisor to the President, David Axelrod.
Republican leaders say, it's early in the game. "We're only at half time. I think that this process is going to play itself out. We will have a nominee, I think, fairly soon, one, two months away," said RNC Chairman, Reince Priebus.
Tracie Potts, NBC News, Washington.