All eyes turn to Illinois in Republican race

In late January, Florida was supposed to be the firewall for Mitt Romney. Then, earlier this month, Ohio was supposed to be the new firewall.

It's now mid-March and another Midwestern state is the new, new firewall for Mitt Romney: Illinois.

Voters in the land of Lincoln head to the polls on Tuesday and the former Massachusetts governor is ahead of rival Rick Santorum, 44 to 30 percent, according to a poll released Monday by American Research Group, Inc.

If Romney pulls off a victory there, he will increase his lead in the all important delegate count. There are 54 delegates up for grabs, but perhaps more importantly, the narrative, is also there for the taking.

Santorum has been getting a lot of attention after his wins in Alabama and Mississippi last week, injecting new energy and momentum into his campaign as he fights to be the only "true conservative" in the race.

But a Romney win in Illinois could make it harder for Santorum to make the case that Romney will not get the 1,144 of 2,286 delegates needed to win the nomination.

A CBS News estimate shows Romney with close to 500 delegates thus far, while Santorum has garnered somewhere between 200 and 250. That means Santorum needs another 900 delegates to win, while Romney needs about 650 additional delegates.

And with every victory for Romney, it makes it harder for any of his challengers to catch up. That's both because there are fewer and fewer opportunities to make up ground, but also because the winner in most states does not get all the delegates and the other candidates can pick up some additional delegates. That's how Texas Rep. Ron Paul has more than 40 delegates, despite not winning in any one state.

On top of that, Santorum is not even eligible for some of the delegate at stake Tuesday in Illinois. The former Pennsylvania senator does not have delegates on the ballot for him in four congressional districts, essentially ceding 10 of the available delegates.

For his part, Santorum has sought to downplay the "math" issue and tried to keep the attention focused on Romney's difficulty in getting the Republican party to unite behind him.

"It's going to be very difficult as this goes on for anybody to get to ... that magic number," Santorum said Monday on "CBS This Morning," referring to the 1,144.

While Romney may have difficulty getting the "magic number," Santorum typically ignores the reality that it is close to impossible for him to get there instead.

Santorum has been stressing his credentials as the only "true conservative" in the race, and said Monday that Romney has no "core" beliefs.

"The convention will nominate a conservative. They will not nominate the establishment moderate candidate from Massachusetts," he said, suggesting that the Republican nominating convention in Florida could be contested.

The Romney campaign fired back, unveiling a web video this month that shows Santorum from four years ago touting Romney's conservative credentials.

"Nobody puts words into my mouth. The words out of my mouth were that if you want a conservative as the nominee of this party, you must vote for Mitt Romney," Santorum said in February, 2008 as Romney was running against Arizona Sen. John McCain for the Republican nomination. Watch the ad here.

Illinois may be the place where he finally begins to build the momentum he needs to avoid a contested convention.