The biggest question in Pennsylvania politics right now isn't whether Gov. Tom Corbett will win reelection. It's whether he'll even get the chance.

Beset by legislative failures and bleak poll numbers, the Republican looks like the country's most vulnerable governor heading into the 2014 election. And Republicans are questioning whether they should let Corbett face a near-certain defeat when they could find a ready replacement with a much better chance of winning.

Already, speculation among GOP operatives has shifted to a quartet of candidates the party might turn to, including several Republicans in the state's congressional delegation. Fearful of alienating a sitting governor, they've done little to publicly jockey for the potential opening. But all are said to be keeping a close eye on Corbett.

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A dramatic move from Corbett to step aside isn't imminent. On Tuesday, he replaced his chief of staff with a veteran political operative. Corbett allies say he remains laser-focused on winning reelection, even if he knows his path to victory is narrow. Meanwhile, Republicans aren't looking to run against him in a primary, only eager to run if he opts not to run for a second term.

But unless Corbett can show improvement in the coming months, Republicans expect the calls for him to step aside to reach a fever pitch. According to one GOP operative in the state, speculation about replacing the governor is "rampant."

"The problem is, you need a path to victory," said one GOP source, who spoke on condition of anonymity to offer his blunt perspective about the governor's situation. "I think they have trouble right now with activists and donors showing them a path to victory. If that doesn't improve in the next couple of months, they'll close their wallets and shut their front doors, and activists and donors will make up their mind for him."

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Another GOP strategist added that Corbett is headed for a "historic landslide [loss]" and rank-and-file party members know it.

"I've never seen anything like this," said the Republican. "Party regulars are just fed up and not willing to help him anymore."

That Republicans are even engaging in such speculation is a testament to how far Corbett has fallen since winning a relatively easy election in 2010. That year, a strong environment for the GOP and the unpopularity of outgoing Democratic Gov. Ed Rendell all but handed Corbett a 9-point victory over Democratic opponent Dan Onorato. The former state attorney general entered office with a solid reputation, personally popular after a successful public-corruption investigation into the state Legislature.

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But as governor, Corbett has disappointed. Conservatives have watched longingly as Republican leaders elsewhere, such as Wisconsin Gov. Scott Walker, pursued an aggressive conservative agenda. Corbett's most ambitious initiative has been privatizing the state-owned liquor-store system, an effort that has so far been stymied despite GOP majorities in the House and Senate. Democrats and moderates have been angered by deep cuts to the state's higher-education system. And small scandals within Corbett's administration—some of them self-inflicted—have routinely distracted voters from his agenda.

Corbett has also been dogged by accusations that, as attorney general, he slow-walked the investigation of former Penn State football coach Jerry Sandusky, who was found guilty of sexually abusing children. The Democratic attorney general, Kathleen Kane, has launched an investigation of her own into how Corbett handled the situation. And in June, a judge threw out an oft-ridiculed lawsuit brought by Corbett that sought to reverse stiff NCAA penalties against the Penn State football program.

Corbett's poll numbers bear the weight of his troubled tenure. An early June survey from Quinnipiac University found his approval rating at just 35 percent. Fifty-two percent of voters said he didn't deserve reelection.

Most alarmingly for the incumbent, however, were his head-to-head performances against a duo of little-known Democratic challengers. He trailed Democratic Rep. Allyson Schwartz, the early front-runner for the Democratic gubernatorial nomination, by 10 points. Against Democratic state Treasurer Rob McCord, he fell behind by 8 points.

Republicans are frustrated with Corbett's plight because many of his problems are self-inflicted. Other GOP governors, such as Ohio's John Kasich, have recovered from previously weak poll numbers and are now in a strong position for reelection.

Corbett's allies fault a poor communications effort from the governor and his staff, a failure GOP operatives say have let Democrats define the governor as an incompetent enemy of the middle class.

"I think Kasich has shown a willingness to sell what he's done in Ohio, and take credit for what's happened in Ohio," said a third GOP operative based in the Keystone State. "And I think the Corbett administration has been much slower and much more reluctant to do that."

Insiders point to four Republicans who could replace Corbett: Reps. Jim Gerlach, Pat Meehan, Mike Kelly, and state Senate Majority Leader Dominic Pileggi. Gerlach and Meehan, both from the suburbs of Philadelphia, ran for the GOP gubernatorial nomination against Corbett in 2010.

Kelly, from the Erie region in northwest Pennsylvania, was a political unknown until unseating Democratic Rep. Kathy Dahlkemper in 2010, but his brash, outspoken personality has made him a standout of that year's conservative class of members. Pileggi is a powerful force in the state Capitol, although he starts with the smallest base of the four possible contenders. He also hails from southeast Pennsylvania.

None of them want to be seen as campaigning for the job while Corbett still plans to run for reelection. But behind the scenes, Republicans are watching closely should any of them make their move.

"Congressman Gerlach fully expects Governor Corbett to be our nominee and he will support him," said Vince Galko, a spokesman for Gerlach. "If the situation were to change, Congressman Gerlach wound give careful consideration to his options."

Even if Corbett opts against running—a big if—the Republican replacement would still have a difficult time winning a general election in the wake of an unpopular administration, a prospect that could scare some of them off. It's why some Republicans think that despite the earnest chatter in private, Corbett will still be the party's nominee in 2014.

And a dwindling number of Republicans remain convinced that, for all his problems, the governor can still pull out victory. Insiders say that Corbett, who held a major fundraiser in Pittsburgh just last week, is expected to raise $25 million to $35 million for reelection, aided by the state's uncapped contributions. That money could be pivotal after a bloody Democratic primary. And Republicans say the administration still has time to gets its message out.

"If we tell the story of Corbett, I think we have an excellent chance of coming back and making it a competitive race," said one Corbett insider, who added that the governor has never given any indication he's thinking of stepping aside.

Meanwhile, Pennsylvania Republican party chairman Rob Gleason was unequivocal that Corbett is running for re-election.

"The Republican Party is united in Pennsylvania to reelect Tom Corbett, grow our dominant 13-member Congressional delegation, and retain control of the State Senate and State House, and our focus is squarely on helping those great leaders and defeating liberal Democrats," Gleason said.

But most Republicans don't share that optimism. One operative who works in Pennsylvania said the situation is worse than the one faced by Sen. Rick Santorum in 2006, when he lost by 20 points.

"Having people talk about if he should run or not isn't where you want to be a year out," said a Pennsylvania-based Republican. "Doesn't mean he won't win next year, but he's in a challenging set of circumstances. The next six months or so are going to be critical in terms what kind of discussion we're having in January of 2014."