The candidate who burst onto the national stage promising to bring red and blue states together is suddenly looking quite blue.
Sen. Barack Obama's second consecutive lopsided loss in a critical swing state has exposed soft spots in the support he's been able to secure.
Key Losses Fuel Doubts
While Obama remains the prohibitive front-runner -- with an effectively insurmountable lead in elected delegates -- those potential weaknesses among key demographic groups are fueling a fierce argument inside the Democratic Party over Obama's ability to win a general election.
The weaknesses constitute Sen. Hillary Clinton's last best shot at the nomination: convincing party insiders who serve as superdelegates that Clinton can turn out the voters who are critical to the Democrats' chances against Sen. John McCain, R-Ariz.
"The bar was set high in Pennsylvania and she got over it with room to spare," said Steve Grossman, a former Democratic National Committee chairman who is helping the Clinton campaign lobby superdelegates. "She's been able to build a broader coalition in each of the last three primaries. And I think that his [Obama's] coalition is more available to her than hers is to him."
Obama Fails to Deliver Knockout Blow
Despite being badly outspent by Obama, the New York senator won a resounding, nearly 10-point victory in Pennsylvania on Tuesday.
It was a statewide Obama wipeout: He carried only seven of the state's 67 counties, primarily in the Philadelphia and Harrisburg areas in the southeastern portion of the state.
"In the big states that count -- that we must carry to win the Electoral College -- she's the best candidate," Pennsylvania Gov. Ed Rendell, a Democrat, said on a conference call with reporters Wednesday. "It was a victory virtually everywhere in the state. … This was an awesome victory, a landslide."
Clinton started making that argument to superdelegates in the immediate aftermath of the primary.
"Last night's win should give a lot of fresh information to our superdelegates," Clinton said Wednesday on ABC's "Good Morning America". "Because, after all, the road to Pennsylvania Avenue does lead through Pennsylvania. And the big win that I had, the broad base of coalition that I put together, is exactly what we're going to need to have in the fall. And, in fact, that's what I've done, in big states, in swing states since this process began."
Clinton's Blue-Collar Coalition
According to exit polls, Clinton carried 54 percent of voters earning less than $50,000 a year; 62 percent of Democrats who don't have college degrees; 63 percent of voters older than 65; and 66 percent of white women.
Clinton ran up similarly wide margins among those demographic groups in Ohio six weeks earlier.
Both states are key to Democrats' November chances; Al Gore and John Kerry both narrowly carried Pennsylvania, and both men would have won their races if they had won Ohio as well.
In one particularly troublesome sign for the fall, only 50 percent of Pennsylvania voters who voted for Clinton said they would definitely vote for Obama if he was the Democratic nominee, according to exit polls.
Twenty-six percent said they would cross party lines and vote for McCain.
Obama aides dismissed such numbers as skewed given the intensity of the primary campaign.
Clinton, they argue, was always favored by Pennsylvania's demographics, and they point out that Obama was behind by about 20 points in polls taken just weeks ago.
David Plouffe, Obama's campaign manager, called it a "flawed exercise" to suggest a direct correlation between appeal in a primary -- with two strong Democratic candidates to choose between -- and likely results in a general election.
"We don't think performance in primaries is the most important measure; it's how you do against McCain," Plouffe said. "We strongly believe that when we do have a nominee, the vast majority of these Democrats are going to come home."
Could Obama Expand Democratic Map?
Obama has run more strongly among white, working-class voters in several other potential swing states, particularly Iowa, Virginia and Wisconsin.
Plouffe cited polls suggesting that Obama got a majority of votes among low-income voters in 14 different primaries and caucuses. He added that recent public polling has shown Obama running stronger than Clinton against McCain in states including Colorado, Iowa, North Carolina, New Mexico and Nevada.
"The best chance we're going to have in the general election is to expand the playing field," Plouffe sad. "We have the organizational ability and the financial ability and the appeal to put a lot of states in play."
But Obama had ample opportunity to make his case in Pennsylvania. With six clear weeks to focus on the state -- and virtually unlimited funds with which he broke campaign spending records -- Obama was still unable to persuade blue-collar white voters to support his candidacy.
Bill Carrick, a Democratic consultant, called it a "strained argument" to claim that a poor primary showing suggests an inability to win a general election race. Still, he said something in Obama's appeal isn't clicking with large segments of Democrats.
"If you try to be objective about the Obama campaign, they're clearly having trouble connecting with white, blue-collar and rural voters," Carrick said. "That's something that, if they can fix in the next two weeks, all these arguments that are giving me heartburn would go away."
Carrick said one problem may be that Obama's main message -- that he'll clean up government and rein in special interests -- rings hollow to voters who are economically struggling and want immediate, practical solutions.
"It clearly doesn't cross over with blue-collar voters and rural voters," Carrick said. "He is not connecting with those voters."
Small-Town Comments Resonate
Further inside the Pennsylvania numbers, the extent of Obama's appeal and limitations becomes more evident.
Clinton carried regular churchgoers as well as gun owners, seven in 10 Catholics and those for whom the economy or health care are the foremost issues.
At a fundraiser in San Francisco in April, Obama told the crowd: "You go into some of these small towns in Pennsylvania, and like a lot of small towns in the Midwest, the jobs have been gone now for 25 years and nothing's replaced them. And they fell through the Clinton administration, and the Bush administration, and each successive administration has said that somehow these communities are gonna regenerate and they have not. So it's not surprising then that they get bitter, they cling to guns or religion, or antipathy to people who aren't like them, or anti-immigrant sentiment, or anti-trade sentiment as a way to explain their frustrations."
According to an analysis of Pennsylvania exit polls by ABC News' polling director Gary Langer, Clinton won small-town and rural voters, 61 percent to 39 percent; weekly churchgoers, 58 percent to 42 percent; and gun owners, 62 percent to 38 percent -- all groups of interest given the controversy over Obama's comment about small-town voters clinging to guns and religion.
McCain has repeatedly labeled the comments "elitist" -- a theme and comments that could be revisited in the fall.
Among other differences with Ohio, Obama did better in Pennsylvania with seniors -- he lost them by 63 percent to 37 percent, better than the 72 percent to 26 percent tally in Ohio. But there were more of them in Pennsylvania, mitigating the change.
Grossman said he believes either Clinton or Obama would beat McCain. But he said concerns voters harbor about Obama would make it more difficult for him to persuade Clinton supporters to stick with a Democrat against McCain, who has strong appeal among moderates and independents.
"I don't believe this divisiveness [will] poison the well," he said. "But I do think that it will be easier for Hillary to win over Obama's base -- African-American voters, better-educated voters, those who oppose the war, who've been with him from day one.… Her coalition is actually growing. His ability to eat into her coalition has grown substantially less robust."
Indiana, with its large portion of white, working-class voters, could provide Obama his best chance to show that he can appeal to voters who have proven resistant to his appeal.
"This election is going to be decided in the middle of the country, by middle-class … voters," said Sen. Evan Bayh, D-Ind., a Clinton supporters. "They want a president who will deliver for them."
ABC News' Gary Langer contributed to this report.