Republicans and Democrats both insist their candidate can win Pennsylvania, which, with 20 electoral votes, is tied with Illinois for the fifth-biggest electoral prize in the presidential election.
But the state has delivered for the Democrat in five straight presidential election wins, making it theoretically more predictable than ten states—Colorado, Florida, Indiana, Iowa, Nevada, New Hampshire, New Mexico, North Carolina, Ohio and Virginia—that have switched allegiances during the last three presidential elections.
Also, Obama's margin of victory in Pennsylvania in 2008 was wider—more than 10 percentage points—than it was in eight other states that supported him and which comprise 97 electoral votes of the 270 needed to win. Meanwhile, Obama lost Missouri by a fraction of a percentage point.
So should Pennsylvania be considered a swing state? Only time will tell.
"Here's what makes us intriguing and a state that will always receive attention," said Christopher Borick, a pollster and professor of political science at Muhlenberg College in Allentown. "While we've gone (to the) Democrat, the races (historically) have been close and the size in terms of electoral votes makes it hard to ignore.
The most recent independent poll, by Connecticut-based Quinnipiac University, showed Obama with a lead in Pennsylvania, 47 percent to 39 percent—a much stronger performance by the Democrat than in two other large states measured by the poll, Florida and Ohio.
For now, Obama and Democratic allies are making a bigger play in Pennsylvania—perhaps because the stakes are bigger here for him: Harry Truman in 1948 was the last Democratic presidential candidate to lose Pennsylvania but win the election.
So far in May, Obama has run three TV ads in Pennsylvania, while a pro-Obama super PAC, Priorities USA Action, has run one. A central part of the strategy seems to be aimed at winning over the blue-collar voters.
Two of the ads warn viewers about the failure of GST Steel, a Kansas City, Mo.-based company that went bankrupt and laid off 750 workers in 2001 after it was purchased by the private equity firm led by Mitt Romney.
A second Obama ad playing in Pennsylvania recounts the country's economic collapse and then its recovery. In particular, it singles out the auto industry, spot-lit by file footage of Obama speaking at what looks like an industrial setting and saying, "Don't bet against the American worker."
Groups that lobby for automakers estimate that 20,000 Pennsylvanians are employed directly or indirectly in manufacturing by the industry, plus another 20,000 in dealerships.
"Pennsylvania is competitive, there's no doubt about that," said Bill Burton, the senior strategist for Priorities USA Action who also worked on Obama's 2008 campaign and at the White House. "I feel he will win Pennsylvania, but it's going to be a fight and we want to make sure we're on the battlefield."
Romney and his super PAC ally, Restore Our Future, spent heavily on TV ads for several days in April until Rick Santorum pulled out of the GOP primary.
Now that the general election campaign is under way, both the campaign and the super PAC have begun running ads, but not in Pennsylvania.
Last week, an independent group that supports Romney, Crossroads GPS, announced ads against Obama in 10 states, including Pennsylvania.
The first ad—it's also running in Colorado, Florida, Iowa, Michigan, Nevada, New Hampshire, North Carolina, Ohio and Virginia—targets various promises that Obama made, and calls those promises broken.
A spokesman for the group, Jonathan Collegio, wouldn't say whether he thinks Romney will win Pennsylvania, or whether the state should be considered a swing state.
"You run an ad where you know citizens and public officials will be paying attention and we know Barack Obama is paying attention to Pennsylvania," Collegio said. "Therefore, that's a great place to run an ad."
Marc Levy covers politics for The Associated Press in Harrisburg. He can be reached at mlevy(at)ap.org.