As former Massachusetts Gov. Mitt Romney tries to cobble together enough delegates to clinch the Republican nomination for president, one potentially big piece — a decisive win in Tuesday’s Illinois primary — may be up in the air.

Illinois should be an easy win for Romney. After all, he has won primaries in Ohio, Massachusetts, Vermont and Hawaii — and he had been expecting to prevail in the Land of Lincoln.

But in recent days, polls point to a tightening race. These surveys show Romney in an increasingly competitive contest with former U.S. Sen. Rick Santorum, thanks in part to the Pennsylvania native’s strength in downstate Illinois. Santorum is planning a weekend swing through southern Illinois, with events in Effingham, Mt. Vernon and Herrin, said deputy campaign director John Hagen.

 Update: Romney is spending several days in Illinois as well. He and his wife, Ann, headlined an evening  campaign town hall in Collinsville.  Romney also highlighted his endorsement from U.S. Rep. John Shimkus, R-Collinsville.

On Monday, Romney is flying around Illinois to deliver a series of speeches focusing on economic issues.

End of update 

Santorum comes into the contest at a disadvantage, thanks to how the state divvies up delegates. He also must deal with the tendency for Republicans in Illinois to gravitate toward moderate candidates.

For at least one observer, Romney’s inherent organizational and ideological advantages make the contest for Illinois’ delegates less exciting than it may appear.

“I think it’s pretty well conceded that Romney’s going to do well in this state,” said Kenneth Janda, a political science professor at Northwestern University. “It is not as receptive to a Santorum message of values as Ohio was.”

Ideological fight

The tussle between Romney and Santorum has been framed by some as ideological. More often than not, conservatives strongly opposed to abortion and same-sex marriage have backed Santorum. Republicans who focus less on social issues tended to go with Romney.

In Missouri, for example, it was Joe Ortwerth, president of the Missouri Family Policy Council, who introduced Santorum after he won the state’s non-binding primary in February. Santorum also held events in Missouri with James Dobson, the president of Focus on the Family.

Jon Zahm, the director of Santorum’s efforts in Illinois, said his candidate is gaining ground for being the “choice of conservative voters.”

Santorum’s delegates and alternates, he said, reads like a “Who’s Who list of the conservative movement in Illinois." That includes people like Dave Smith of the Illinois Family Action, Penny Pullen of Eagle Forum Illinois, Irene Napier of McHenry County Right to Life.

“I could go on and on with the endorsements and support of the conservative movement leaders that we have, and that’s what’s driving our success here in Illinois,” Zahm said. “We’re wired here on the ground and have an extremely strong team.”

Meanwhile, Romney has the support of several elected officials, including U.S. Sen. Mark Kirk. Kirk — a former congressman from suburban Chicago — is one of the more moderate lawmakers in the U.S. Senate, having expressed support  for abortion rights and gun control. Kirk, who is recovering from a stroke, is not actively campaigning for Romney.

Romney’s campaign also has the support of Illinois Senate Minority Leader Christine Radogno, a Republican from the Chicago suburbs who also has supported abortion rights in the past. Radogno joined state Treasurer Dan Rutherford on a conference call Tuesday discussing Romney's efforts in Illinois.

“I firmly believe (Romney) is the best person to lead this country, and I base that on his experience,” Radogno said. “He has private sector experience. He understands the need to get the economy righted in order to continue with job creation. And secondly, he’s also been a governor in a state where he had to work closely with another party. And we all know that’s a challenge in Washington, D.C.”

In some ways, the fight between Santorum and Romney mirrors the struggle between moderates and conservatives within the Illinois Republican Party. Sometimes, the conservatives have emerged victorious, such as when Peter Fitzgerald managed to wrestle away a U.S. Senate seat from Carol Mosley-Braun in 1998. And more recently, Republican Bobby Schilling — a favorite of the Tea Party — won a seat in Congress in the 17^th District.

But more often than not, Republicans in Illinois have tended to select moderate candidates. For instance, the last three Republican governors of Illinois — Jim Thompson, Jim Edgar and George Ryan — tended to govern less conservatively than their national counterparts.

Winner doesn't take all

Earlier this week, Santorum won both Mississippi and Alabama. But even  Santorum got the most votes, both Mississippi and Alabama allocate delegates proportionally. That means that Romney’s delegate lead actually expanded, especially since he prevailed in contests in Hawaii and American Samoa.

It’s entirely possible that Santorum could win Illinois’ popular vote but snag fewer delegates than Romney. According to Ken Menzel, deputy counsel at the Illinois Board of Elections, here’s how Tuesday’s primary works:

• Republican voters will make a selection among presidential candidates. Menzel dubbed this part of the primary a “beauty contest,” since the winner gains no advantage whatsoever in determining delegate allocation.
• Voters will then select between two and four delegates pledged to a certain candidate in each congressional district. It is entirely possible, Menzel said, for a voter to select Romney in the “beauty contest” and then vote for delegates of another candidate.

Santorum’s campaign failed to submit slates of delegates in four congressional districts, including three Chicago-area congressional districts. Santorum delegates also won’t be on the ballot in the 13^th District, which encompasses Metro East cities such as Alton, Edwardsville and Collinsville.

That means Santorum is only eligible to win 44 out of the 54 delegates up for grabs on Tuesday. The other 15 delegates aren’t picked through popular election.

“The population center in Chicago is far more of a Democratic territory than Republican territory,” Janda said. “I think Romney will do really pretty well up here, probably Santorum will have some appeal downstate. But he has not filed delegates in all of the congressional districts. So that puts him at a handicap. … Even if he were to do relatively well, there are some places where he could theoretically win and not have any delegates.”

The Daily Herald even reported that Santorum was short of the needed signatures in numerous other districts. But Romney’s camp decided not to put up a challenge.

Rutherford said on Tuesday’s conference call that Santorum will have trouble in the race for delegates.

“Even from the beginning, he’s going to be behind in even having eligible candidates,” Rutherford said. “The other thing that I would note is the candidates that are running for delegate and alternate for Gov. Romney are people that are profiled, experienced, known people within their area. [There’s] a number of legislators, a number of former legislators.”

But Zahm said Santorum plans to contend well in downstate Illinois and some Chicago suburbs. Besides his stops in downstate Illinois, Santorum will make a stop in the Chicago suburbs later this week.

“Frankly, the only place where Gov. Romney has any kind of strength is in the city of Chicago, where the voters tend much more moderate to liberal,” Zahm said. “We’re not seeing problems in the suburbs at all. In fact, our campaign office is in Elgin, which is at the confluence of three districts — 6^th, 8^th and 14^th. And we’re doing well in those districts and feel very good about our chances there.”

While both Gingrich and Paul are campaigning in Illinois, Janda said neither candidate is expected to pick up any delegates.

And more importantly, Janda said, it’s unlikely that the winner of the Illinois primary will be able to make much headway in the fall. President Barack Obama — who is from Chicago — won the state in 2008 with nearly 62 percent of the vote.

“There’s not a real question of how the state will go in the general election,” Janda said. “It’s most likely going to go for Obama. So it’s unlike Ohio where there was added interest in the primary because of its status in the general election.”