VERNON HILLS, Ill. — Same story, different state. 
 
 Mitt Romney has a roster of blue-chip GOP supporters here, more resources and a superior organization in a state that seems a good fit to his brand of Republicanism. 
 
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 And yet again, on primary eve, Illinois remains in play, with Rick Santorum seemingly within striking distance and the former Massachusetts governor’s local supporters more nervous than they should be about Tuesday’s outcome. 
 
 Bob Michel, the former House GOP leader who served 19 terms in Congress representing Peoria, acknowledged that Romney has thus far failed to generate sufficient excitement to deliver a convincing knockout blow to Santorum in Illinois. 
 
 “He’s not overwhelming, that’s the problem through the whole damn primary,” said Michel, who backed Romney in 2008 and again this cycle. “What’s the spark? What’s the thing that gets him off and running? No one knows.” 
 
 Romney’s inability to lock down the Republican vote in the most populous of the Midwestern states is exemplified by former GOP Gov. Jim Edgar’s ambivalence toward him. 
 
 The former two-term Illinois governor should be in Romney’s sweet spot: He’s a pro-business Republican who held statewide office for 18 years and sometimes faced trouble from more orthodox conservatives. 
 
 But rather than backing Romney, Edgar is sitting out a Republican presidential race, he said, for the first time since getting into elective politics. 
 
 “Romney just doesn’t get folks real excited,” Edgar told POLITICO. “It seems like he can get about 33 percent and just about hovers there.” 
 
 A moderate in the tradition of successful statewide Republicans dating from Everett Dirksen to Thompson to Sen. Mark Kirk, Edgar said Romney’s tack to the right on a range of issues since becoming a national candidate leaves him vulnerable of blurring the lines between him and Santorum. 
 
 In a state without formal party affiliation, where voters choose one party’s primary ballot at their precinct, Edgar said Romney may have cost himself support by wooing the GOP’s most conservative voters. 
 
 “If he keeps moving to the right, I think he might be losing some people who are saying he’s not a whole lot different than Santorum,” Edgar said. “If Romney was kind of running with his governor of Massachusetts image, then he might get some Democrats and independents to come in and help him. But today, I don’t know.” 
 
 Romney’s Illinois team — which has long expected to win the state — now has him campaigning here like a candidate scared. A Chicago Tribune/WGN poll taken March 7-9 showed Romney’s lead over Santorum at 4 percentage points, with Newt Gingrich and Ron Paul far behind, though a Public Policy Polling automated survey released Sunday evening gave Romney a more comfortable 15-point edge. 

 Mitt Romney is headed for a blowout victory in Illinois on Tuesday. He leads with 45% to 30% for Rick Santorum, 12% for Newt Gingrich, and 10% for Ron Paul. 
 
 Romney's particularly strong among voters who live in suburban areas (50-29) and with those who live in urban areas (46-23). But he's even running slightly ahead of Santorum, 38-36, with folks who identify as living in rural parts and that strength with a group of voters he hasn't tended to do that well with is why he's looking at such a lopsided margin of victory. 
 
 Romney tends to win moderates in most states and Santorum usually win voters describing themselves as 'very conservative.' The swing group in the Republican electorate is those identifying as just 'somewhat conservative.' Romney is winning those folks by a whooping 60-20 margin in Illinois. Romney's also benefiting from a 52-28 advantage with seniors. 

 WHEATON, Ill.—The Land of Lincoln once proved a reliable home for centrist Republicans, making it the kind of state Mitt Romney would have carried comfortably. 
 
 Not anymore. The former Massachusetts governor finds himself locked in a dogfight here with former Pennsylvania Sen. Rick Santorum ahead of Tuesday's primary, thanks in part to the rising influence of more-conservative Republicans. 
 
 Enlarge Image Close Getty Images Mitt Romney and his wife, Ann, are introduced at a pancake brunch Sunday at an American Legion post in Moline, Ill. 
 
 GOP presidential candidate Mitt Romney blasted former Senator Rick Santorum as an "economic lightweight" during a campaign stop in Illinois Sunday. Romney said the nation needs an "economic heavyweight" in order to turn the country around. (Video: NewsCore/Photo: Getty Images) 
 
 In 2010, this shift to the right resulted in five new Republicans riding the tea-party wave to Congress from Illinois. The same year, a socially conservative candidate survived a crowded primary for governor only to lose in the general election to the Democratic protégé of jailed former Gov. Rod Blagojevich. 
 
 Now, the development of a conservative power center in the party is being mirrored in the presidential race, as Messrs. Romney and Santorum barnstorm the state. Mr. Romney has touted his endorsements by Illinois elected officials—the treasurer and several House members among them, along with former House Speaker Denny Hastert—while Mr. Santorum has been trying to tap into the frustration that many conservative activists say they feel with party leaders. 
 
 "All the Republican establishment, as you know, is lined up behind Romney," Mr. Santorum told a crowd of roughly 2,000 at a rally Friday in the Chicago suburb of Arlington Heights. "Hopefully, the conservative voices here in the state will say that the best chance for us to beat Barack Obama is to have a clear choice," he added, saying that Mr. Romney's policies were too similar to the president's. 
 
 Mr. Romney campaigned in Moline on Sunday and focused on Mr. Obama, linking his policies to rising gas prices. Newt Gingrich campaigned in Illinois last week, as did Rep. Ron Paul. 
 
 The influx of conservative activists has led to more infighting and produced mixed results for the party statewide. The House gains in the last election were offset by the GOP's failure to recapture the governorship, despite a wave of embarrassing political scandals for the Democrats. Republican Bill Brady, the most conservative candidate, eked out the nomination as his more centrist rivals split the vote, but he lost in the general election, in part because he had a record on social issues that soured suburban voters. 
 
 "Illinois is a conservative state, but we're not a right-wing state," said Republican former Gov. Jim Thompson. "Every time we elect a right-wing candidate for governor, they lose." 
 
 By contrast, Cynthia Schneider, a Santorum delegate from the Chicago suburb of Naperville, thinks the Republican establishment in the state remains far more moderate than the party as a whole. Mr. Romney finished second in the 2008 GOP primary in Illinois, though he was competing with another centrist in Sen. John McCain. 
 
 The state's recent travails have provided ample fuel for Republicans here. Last year, Democrats in the statehouse approved a 66% increase in state income taxes to patch a looming budget shortfall. Even so, Moody's Investors Service dropped the state's credit rating earlier this year, to the lowest in the country. 
 
 At the same time, the state continues to lose businesses to its neighbors, such as Indiana and Wisconsin, which actively court Illinois companies. The unemployment rate of 9.4% is one of the country's highest. 
 
 "People are mad," said Rep. Judy Biggert (R., Ill.), who represents the western suburbs of Chicago and supports Mr. Romney, saying he has the best plan to cut the deficit. "They're really focused on debt and government spending." Others say the angriest voters are likely to back Mr. Santorum. 
 
 Illinois hasn't played a major role in a Republican nominating contest since 1988, when voters here sided with then-Vice President George H.W. Bush over then-Kansas Sen. Bob Dole. Officials here say the presidential campaigns seem almost surprised that they have wound up competing in Illinois this year, and they see little evidence of robust get-out-the-vote operations. That could benefit Mr. Santorum, since conservative activists seem the most eager to vote and would carry more influence in a low-turnout election, Republican officials say. Turnout projections for Tuesday vary, however. 
 
 Here in Wheaton, a Chicago suburb, yard signs touting primary contenders for various state and local offices clutter most busy arteries, but the names Romney and Santorum are conspicuously absent. 
 
 Roughly three-quarters of all Republican votes in the state come from the Chicago area, which stretches far out from the city. But towns like Wheaton and nearby Naperville aren't on the itinerary of the two leading presidential candidates. 
 
 "If I were running the campaigns, I would have fired someone by now," said Patrick Durante, a Republican operative in this part of the state. "They clearly thought this thing would be wrapped up before Illinois." 
 
 Likewise, voters and local political operatives say the candidates have not devoted much time or money to phone calls or mail; instead, a super-PAC supporting Mr. Romney has spent nearly $2.5 million on television ads in the state, while a group supporting Mr. Santorum has spent roughly $300,000. 
 
 Mr. Roskam said he didn't see much presence of either campaign during the two St. Patrick's Day parades he walked over the weekend in Republican-friendly DuPage County. 
 
 Write to Douglas Belkin at doug.belkin@wsj.com and Patrick O'Connor at patrick.oconnor@wsj.com 
 
 A version of this article appeared Mar. 19, 2012, on page A4 in some U.S. editions of The Wall Street Journal, with the headline: Illinois Race Muddled by State's Move Right.
– A new poll puts Mitt Romney 15 percentage points ahead of his closest rival, Rick Santorum, in Illinois' primary tomorrow—but perhaps he shouldn't start celebrating yet. Public Policy Polling has Romney winning 45% of the vote to Santorum's 30% (it puts Newt Gingrich at 12% and Ron Paul at 10%), noting the former Massachusetts governor is dominating the electorate's "swing" group—those who call themselves "somewhat conservative." But read this morning's papers, and you'll find a much gloomier take on the situation, with many saying Romney's effort in the state hasn't been convincing. "He’s not overwhelming, that’s the problem through the whole damn primary," former House GOP leader Bob Michel tells Politico. Former Republican Gov. Jim Edgar hasn't backed Romney, despite being a fellow pro-business moderate. "It seems like he can get about 33% and just about hovers there," Edgar says. The Wall Street Journal reports Romney is "locked in a dogfight," citing a recent shift to the right in the state. The New York Times echoes that take, noting a growing conservative bloc and writing that "Illinois is not shaping up to be the effortless romp some had presumed."