Tom Corbett is about to make history.

On Tuesday, the Republican will either be the first Pennsylvania governor to lose a reelection try since the 19th century, or he will overcome a double-digit polling deficit with an unprecedented late surge.

Corbett and Democrat Tom Wolf have entered the mobilization stage of the campaign, traveling the state to push their partisans to turn out, a harder task in a midterm race than in a presidential year.

Both are bringing high-powered motivational help to the region Sunday evening. President Obama will headline a rally at Temple University, and Gov. Christie, a likely 2016 contender for the White House, will campaign for Corbett in Bucks County.

Obama's approval rating was just 32 percent statewide in last week's Franklin and Marshall College Poll, but Wolf strategists believe the president's continuing popularity in the city will help build the kind of vote margin he needs there in order to win.

Overall, Corbett has cut into Wolf's lead but still trails by double digits among likely voters, according to the F&M survey and another released Friday by Muhlenberg College: 13 and 12 percentage points, respectively.

Sourness toward Obama is boosting Republican efforts to take control of the U.S. Senate, but in Pennsylvania, sizable majorities of voters in poll after poll also disapprove of Corbett's performance and think the state is on the wrong track.

"They kind of balance each other out," said F&M pollster Terry Madonna.

Last week, Corbett's campaign began airing a new ad that links Obama to Wolf, saying that the York businessman is a liberal who supports the president's "radical agenda." A vote for Wolf is like voting to make Obama governor, the ad says.

And the campaign kept hammering what has become its main theme that Wolf would increase taxes, seizing on the Democrat's expressed desire to reduce the state's flat 3.07 percent income tax for lower and middle-income people while increasing it for the wealthy. He also has promised to boost the state's share of schools funding from about one-third to half the cost, and wants to shift the overall tax burden to reduce reliance on property taxes, which notoriously hit lower-income homeowners hardest.

Steep hill

Wolf, meanwhile, has kept up a barrage of ads reminding voters of steep cuts in state education spending early in Corbett's term; of his refusal to tax drillers on the value of the natural gas they are taking from Pennsylvania; and of the state's relatively slow rate of job creation, despite Corbett's business tax cuts.

Indeed, the campaign has remained focused on these issues since it began, with the fear of tax hikes giving Corbett a wedge that, strategists say, has helped him close the gap by increasing his soft support among Republicans.

When he defeated Democrat Dan Onorato by about 9 percentage points in 2010, a Republican year, exit polls showed that Corbett captured the votes of 15 percent of self-identified Democrats. He got 93 percent of Republicans.

The F&M poll, released Wednesday, found Corbett with the backing of 75 percent of Republicans and just 7 percent of Democrats.

That's a steep hill to climb, said Philadelphia-based Democratic strategist Neil Oxman, who worked for Onorato four years ago.

Expensive battle

"This race was never about Tom Wolf - it's about Tom Corbett's upside-down likability and job-approval numbers," Oxman said. "It's always been a referendum."

In the last 30 years of reliable state-level polls no candidate for governor who was behind by 10 percentage points or more five days from election day has come back to win, said Chris Borick, pollster for Muhlenberg College.

"We don't have one on record," Borick said. "There's not even an outlier. Corbett would be it."

To do that, however, the governor has to hope for the "total collapse" of Democratic turnout - and much more. "He needs to win back Republicans who haven't embraced him, and to convert voters who are headed to Wolf," Borick said. "That's hard to do in the last few days."

It's been an expensive battle.

The candidates and independent groups have combined to spend an estimated $47.4 million to run nearly 50,000 television ads on broadcast and national cable channels in Pennsylvania as of Oct. 27, according to the Center for Public Integrity.

It was the fourth highest total in the nation.

Wolf spent $17.7 million to buy ads that ran 23,472 times, while Corbett spent $14.2 million on 22,077 ads.

Pa. Families First, an independent-expenditure group affiliated with the Democratic Governors Association, spent $1.8 million to run 2,302 ads in the summer, attacking Corbett for cutting education spending.

NextGen Climate Action, the political arm of San Francisco hedge-fund tycoon Tom Steyer, spent $1.1 million blasting the governor; the Philadelphia Federation of Teachers spent $1 million.

The major national conservative groups have stayed out of the race, but Corbett benefited from $220,500 worth of ads run in October by Key Questions, Key Answers, a group affiliated with conservative leader Colin Hanna, a former Chester County commissioner.

Wolf's spending includes the Democratic primary, when he put up $10 million of his own money and built an enduring image from his story as your average small-town Jeep-driving businessman with a doctoral degree from MIT. He won the primary going away and began with a lead against the incumbent, in his first campaign for elective office.

Corbett tried to turn his budget-cutting into a virtue in the campaign, saying he was elected to "change the culture" in Harrisburg and wasn't aiming to be liked. He was the eat-your-vegetables governor.

He got a potential boost late Thursday night, when law enforcement officers captured accused cop-killer Eric Frein in the Poconos after a seven-week manhunt. Corbett was live on the networks and national cable announcing the good news - a vivid reminder of his past as two-term state attorney general.

On Friday, Corbett swung through the solidly Republican south-central Pennsylvania.

He repeatedly linked Wolf to the policies of Obama and the "tax-and-spend" former Gov. Ed Rendell, while hammering home his "underdog" image to energize voters in the final stretch. "All the pundits said I couldn't win in my other races," Corbett told voters in Carlisle. (In fact, the Associated Press wrongly called his first race for attorney general for his opponent, Democrat Jim Eisenhower, in 2002. But Corbett was the front-runner in his second run for attorney general, and in the governor's race in 2010.)

Bob Wollyung, a retired sheriff and state trooper who is now chairman of the Franklin County Republican Party, said Corbett deserves reelection because he has strong character and a great pro-business philosophy.

"People are fed up with politics on both sides, but if they knew our governor they wouldn't be. I think he's being honest," he said. "I'm against Wolf because we're taking enough of people's money as it is."

Wolf rallied the Democratic faithful Friday at several stops, including one in Phoenixville, where he spoke for about 15 minutes to a crowd of volunteers and representatives from organizations such as Planned Parenthood and the Pennsylvania AFL-CIO.

"I'm a little nervous," said Doug Gunn, of Phoenixville, who has been volunteering in Wolf's get-out-the-vote efforts. "I'm afraid the drop-off in a midterm election is going to hurt the Democrats."

If it hurts enough, Corbett could dodge a historic fate. The last gubernatorial incumbent to lose was William Bigler, a Democrat.

That was in 1854.

In the 'gayborhood,' at the gun show: Wolf, Corbett implore supporters to turn out Tuesday

The tableau was memorable: As Friday night turned to Saturday morning, a former Pennsylvania governor and a possible future governor serenaded a packed piano bar in Philadelphia's "gayborhood."

Ed Rendell, accompanied by pianist Ghosha D'Aguanno, sang "Close to You." Tom Wolf, running for governor, said he hadn't been asked to sing solo in 50 years - and then sang "I'll Never Fall in Love Again."

The two Democrats toured the gayborhood's night spots, aiming to rally a Tuesday turnout for Wolf. The response was enthusiastic.

"I am awed by it," John Giuliano, 64, a Widener University social-work professor who lives in Bala Cynwyd, said after the singing. "I just think it's wonderful they came to get our vote, even though they know they have it."

On the final weekend of their campaigns, Wolf and his Republican opponent, Gov. Corbett, were reaching out to the loyalists that politicians call "the base."

Wolf spent much of Saturday in heavily Democratic Philadelphia, hitting rain-soaked rallies from Germantown to West Philadelphia to a supermarket in Point Breeze, where 40 union members chanted, "We want Wolf!"

Eighty-eight miles west, Corbett, too, was working a friendly crowd, going from booth to booth Saturday morning at a gun show attended by hundreds in Lebanon.

The event came as a Corbett campaign adviser, speaking on condition of anonymity, confirmed that the National Rifle Association was urging its 250,000 Pennsylvania members via e-mail to vote for Corbett. The NRA grades candidates - it gave him an A and Wolf an F.

At the gun show, vendors and visitors alike approached Corbett, telling him as he strolled the sprawling Lebanon County Expo Center, "You've got my vote."

His day began with a visit to a Baptist church in Harrisburg and ended with get-out-the-vote stops at small businesses in Schuylkill County and rallies in Luzerne County.

Before Corbett left the Lebanon event, vendor Anne Rickert of My Liberty Threads offered him a T-shirt, but he pulled out a $20 and said, "It's better if I paid." When someone held up an iPhone to take a picture, Corbett quipped, "Make sure you can see that I'm the one giving her the $20."

The shirt he bought was emblazed with an American flag and the words "It's We the People - not You the Government!"

Corbett, who won the governorship in 2010 on a pledge to cut the cost of state government, said to those around him: "Isn't that what I've been talking about?"

INSIDE

The governor's race aside, it looks like the GOP's day. A16.

Foes of legal pot are smelling victory. A4.

Christie's style

is back on full, forceful display. B4.

Four races will decide control

of the Pa. senate. Currents, C1.

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Inquirer staff writers Amy Worden and Jason Laughlin contributed to this article.