Senator Barack Obama is marching into Pennsylvania as something he hasn't been in a while: the underdog. Senator Hillary Clinton is ahead of her fellow Democrat and rival by an average of 17 points at the polls, according to RealClearPolitics.com.

Clinton has done well with older voters, blue-collar workers and rural voters. The Keystone State has the second-oldest population in the country, a large working class and miles of farmland that produce crops as varied as mushrooms and Christmas trees.

"I think it is probably a state she should win in just about any circumstance," said Vaughn Ververs, senior political editor at CBSNews.com. "Of course, this campaign is a much different circumstance than we've ever seen, and I don't think anything can be taken for granted in this environment."

On Tuesday (March 18), Obama led Clinton in the delegate count, but only by about 139, according to CNN, and neither candidate is within striking distance of the 2,024 delegates they need. With 188 delegates up for grabs, neither of the candidates can afford to take any part of Pennsylvania for granted. So while Pennsylvania is pretty much Hillary Clinton's race to lose, there are quite a few variables at hand in a state that Democratic pundit James Carville described as "Pittsburgh in the west, Philadelphia in the east and Alabama in the middle."

One of the most important variables in this campaign is time; Pennsylvania's primary isn't until April 22. We have not seen so much time between two critical competitions since primary season started in Iowa on January 3.

Barack Obama has done pretty well at closing popularity gaps when he has time to campaign in a state. He was way behind in Ohio and Texas weeks before those states' primaries, but ended up almost catching up to Clinton. He merely narrowed the gap in Ohio, but in the Lone Star State, Obama ended up winning more delegates than Clinton while narrowly losing the popular vote.

The time factor could also help the Obama campaign with some of its most crucial demographics in Pennsylvania, including young and first-time voters. Voter registration in Pennsylvania doesn't close until Monday.

"The bulk of our campaign, almost all of it, has been focused on voter registration in the last three or four weeks, and it will continue to be voter registration until March 24th," said Sean Smith, a spokesperson for Obama's Pennsylvania campaign. "And a lot of that registration is around college campuses and with young voters."

Pennsylvania's laws for voter registration require that you live in the state for at least 30 days before the election, so out-of-state college students can vote in the upcoming primary as long as they have not registered to vote in other states.

"If they are eligible to vote here, we are doing everything we can to register them," Smith said. "College students absolutely could [bridge the gap for Obama]. If they turn out in the kinds of numbers that they've turned out in other states, they could really help us out here."

But Pennsylvania's young voters may not be enough for the Illinois senator. "You can count me among those who were skeptical about the impact of young voters in this campaign until they actually started to show up in large numbers and things started happening," said CBSNews.com's Ververs. "I think that it is probably not enough to get him over the top. He's going to have to woo some of those rural, older voters."

Hillary Clinton's campaign had not responded to MTV News' request for comment on its Pennsylvania campaign strategies by press time.

More time may mean Obama has more time to register young voters and woo folks on the farm, but it also means that there will be more time for the public and the press to ask him questions. He has recently had to spend more time answering questions about his relationships with a controversial pastor and an allegedly corrupt supporter than about the economy and the war.

"The danger for him is kind of a 'drip, drip, drip' effect. Is there anything else that is going to come out?" Ververs wondered. "It's less of a danger for Clinton than Obama, because he hasn't been through that sort of a process yet. I think people are more used to it with her."

One last variable to worry about is what kind of campaign we will see in Pennsylvania. Will it be a knock-down, drag-out fight with mudslinging like we saw in South Carolina? Or will the candidates tone the rhetoric down a notch and be more civil with each other, as we've seen them at some recent debates?

"There are a lot of high-profile Democrats nowadays who would like them to tone it down a little bit," Ververs said. "They see this as potentially being divisive, in that whoever doesn't win this contest, their supporters will be a little hardened and angry because it is too negative."

That division could lead to a lack of support for the nominee when it comes time to face presumptive Republican candidate, Senator John McCain. The Democrats are having enough problems with irritated voters in Florida and Michigan, since the party has still not reached compromises with those states about seating their delegates at the convention in August. The last thing they want are disillusioned Democrats worn out by a hard-fought, never-ending primary.

There are still nine more primaries to go for the Democrats after Pennsylvania's on April 22.