By Mary Wisniewski and Edith Honan

(Reuters) - Illinois, the longtime home of President Barack Obama, has chosen Democrats for president in every election since 1992 and for governor since 2002. But this year Republicans, finding a weak incumbent in Democratic Governor Pat Quinn, see an opening.

The Republican front-runner ahead of the March 18 primary, venture capitalist Bruce Rauner, has emerged as a deep-pocketed and potentially formidable rival. The Republican National Committee already has staff on the ground in Illinois and plans to add more this spring.

Quinn eked out a victory four years ago by less than 1 percentage point and his job approval rating has hovered around 34 percent as voters complain about the state's anemic job growth and hobbled economic recovery.

In recent months, Quinn's fortunes have improved thanks to passage of a pension reform bill and after former White House Chief of Staff Bill Daley, brother of the longtime Chicago mayor, abandoned a short-lived primary challenge. But political insiders still view Quinn as vulnerable.

"Quinn is in deep trouble and the closer we get to November, the more vulnerable he looks," said RNC spokesman Ryan Mahoney.

Public Policy Polling has called Quinn's re-election chances a "toss-up," while the Cook Political Report favors Quinn based on Democrats' heavy registration advantage in the state, much of that in the state's largest city, Chicago.

"The governor benefits from being in a state that is definitely Democratic-leaning," said Kent Redfield, a professor at the University of Illinois at Springfield. "I think the governor is perceived as being honest and sincere, but not a strong, forceful leader."

Quinn took office in 2009, stepping up from the lieutenant governor's chair after the impeachment of then-Governor Rod Blagojevich, who was removed from office and is serving a 14-year sentence for political corruption.

The following year, Quinn narrowly defeated Republican State Senator Bill Brady, a social conservative, winning by fewer than 32,000 out of 3.4 million votes cast.

In his first full term, Quinn pushed through a pension reform measure and an income tax hike and signed laws legalizing same-sex marriage and medical marijuana.

But voters faulted him for struggling to reach deals even with lawmakers from his own party. The ultimately successful battle to pass major pension reform late in 2013 took place among legislative leaders, with no major public role for Quinn.

But such are the politics in Illinois that the Democrat's unpopularity does not necessarily translate to unelectability.


Rauner has momentum on his side, political watchers say.

He has set a state record for primary spending, pouring $6 million of his own money into the race while raising millions from donors. Ads depicting him as a straight-talking anti-politician have dominated the state's TV airwaves, while his rivals lack the funds for a major broadcast ad campaign.

On the campaign trail and in candidate forums, Rauner avoids talking about social issues and offers a populist platform of more jobs, lower taxes, better schools and term limits. Passage of pension reform took away one of his major rallying cries — the inability of Quinn to deal with the state's pension crisis.

The state's airwaves are hardly an all-Rauner affair. A group of public employees' unions has contributed heavily to Illinois Freedom PAC, which has funded anti-Rauner television ads.

A February Chicago Tribune/WGN-TV poll had Rauner leading his Republican rivals with 40 percent support, more than his two main rivals combined.

"Rauner's hired good people. He's been incredibly disciplined. He's been on the air constantly," said Redfield.

He has also made rookie mistakes.

After voicing support for lowering the Illinois minimum wage, Rauner faced heavy criticism and changed his position.

His rivals for the Republican nomination include Brady, who hopes for a re-match against Quinn and State Senator Kirk Dillard, a suburban moderate who served as chief of staff for the popular former Republican Governor Jim Edgar.

State Treasurer Dan Rutherford is also running, but his candidacy has been badly hobbled by allegations of sexual harassment leveled against him by a former male staffer.

The other candidates accuse Rauner, who reported a 2012 income of $53 million on his tax forms, of trying to buy the nomination. In a forum this week, Rauner said the limit to his spending is "winning the race."

Still, political analysts say Quinn has the edge. And, for all his own spending, Rauner's opponents are likely to invest heavily in his defeat.

"Rauner will have tons of money, as we've seen, but I think there will be a lot of money coming in to help Quinn, particularly from national unions," said political consultant Don Rose.

(Reporting By Edith Honan; Editing by David Greising and Cynthia Osterman)