IS OBAMA JFK OR ADLAI STEVENSON? (E.J. Dionne, Washington Post) The result of the 2008 election may come down to how voters decide to define Barack Obama. Is he Adlai Stevenson or John F. Kennedy? Is he a detached former law review editor or a passionate agent of change? Is he an upscale reformer focused on process or a populist who will turn Washington and the country around? One of the central lessons of the Pennsylvania primary campaign is that Obama’s personality is now far more important than either Hillary Clinton’s or John McCain’s. That’s true not only because voters have a longer history with Clinton and McCain, but also because so much of the energy and novelty of 2008 is the product of Obama’s rapid breakthrough to wide acclaim.

OBAMA PREPARES TO SPIN LOSS AS VICTORY (Ben Smith, Politico) Barack Obama could have had a worse Pennsylvania primary. DNA tests could have revealed Tony Rezko to be his father. David Axelrod could have absconded with $40 million from his campaign treasury. He could have bowled a 36. Hillary Rodham Clinton, on the other hand, could hardly have dreamed of a finer time to tout her Scranton roots in one of her several home states. The seven-week gap between primary contests began with video of Obama’s former pastor shrieking that “America’s chickens have come home to roost” and ended with Obama explaining his way out of what sounded like an insult to the gun-owning, God-fearing Democrats of central and western Pennsylvania during a debate that amounted to a 3-on-1 grilling. But instead of deteriorating into a snoozer of a Clinton blowout, polls that had her up an average of 16 percentage points in mid-March now show her up an average of just 6 points. And both camps — including a visibly energized Obama campaign in recent days — are now preparing to spin Tuesday’s results as a victory.

WHAT TO LOOK FOR IN THE PENNSYLVANIA PRIMARY (Peter Wallsten, Los Angeles Times) In what may seem like a paradox, the Clinton victory predicted by nearly all public opinion polls might actually turn out to be a loss if she doesn’t win by a significant margin. And if Obama keeps the results closer than some surveys suggest, he could be considered victorious – unless it appears that Clinton’s campaign has succeeded in casting doubt on his credentials to be commander in chief or his ability to win support in the fall from white, working-class voters. Here are some factors that, in addition to who wins the vote, will help decide whether the Pennsylvania primary is one more way station on the road to the final primaries in June, or whether the nomination fight might come to a quicker conclusion: the spread… the demographics… the delegates… the electability question.

MORE: 5 Things to Watch in the Pennsylvania Primary (Politico) Check for turnout at 1 p.m.; don’t be fooled by early results; follow the undecideds; watch these towns and neighborhoods; key counties to keep an eye on.

CLINTON, OBAMA MAKING LAST PITCHES TO PENNSYLVANIA (Anne E. Kornblut and Paul Kane, Washington Post) Sens. Hillary Rodham Clinton and Barack Obama offered Pennsylvania voters their closing arguments on Monday, winding down a nearly two-month campaign in the state that has done little to bring clarity to the Democratic presidential contest. In stops statewide, Clinton continued to say that she is best prepared to serve as president, while Obama and his aides sought to play down expectations for a race in which victory appeared to be slipping out of his reach.

8 QUESTIONS ABOUT THE PENNSYLVANIA PRIMARY (Dan Balz, Washington Post) What will it take to be declared the winner in Pennsylvania today? Has the campaign weakened Obama or Clinton more for the general election? What is Obama’s biggest general-election vulnerability? Has Bill Clinton helped or hurt his wife’s candidacy? What is the most important remaining contest after Pennsylvania? Will Democratic superdelegates coalesce, or could this go to the convention? Could there still be a Democratic dream ticket? Has John McCain used this period effectively to get ready for the general election?

DREAM TICKET SOUNDS GOOD TO MANY DEMS (EXCEPT THE CANDIDATES) (Patrick Healy, New York Times) For months, the Clinton and Obama campaigns have been hearing suggestions of a so-called dream ticket of Obama/Clinton or Clinton/Obama. Former Gov. Mario M. Cuomo of New York has pressed the idea most aggressively — it also came up in last week’s debate — while a major Clinton supporter in Tuesday’s Pennsylvania primary, Gov. Edward G. Rendell, has blessed it, too. And some uncommitted superdelegates — the party leaders and elected officials whose votes may determine the nominee — see such a unity ticket as a way to short-circuit a fight for the nomination all the way to the Democratic convention in August, and to blend the voter bases of the two candidates… All that stands in the way are a few pesky details — like the fact that Mr. Obama and Mrs. Clinton want to be done with each other, starting now. And that Mr. Clinton bitterly believes that the Obama camp has portrayed him as a brutish, race-baiting campaigner, according to two associates of Mr. Clinton. On top of that, Obama aides assert, Mrs. Clinton’s baggage would damage Mr. Obama’s image in a New York minute. And they also believe that the Clinton camp’s negative tone seems a poor match for Mr. Hope. To be precise, aides for both candidates would not rule out the idea of a joint ticket — though it was hard to hear it through all the laughing.

IN CLINTON VS. OBAMA, AGE IS A GREAT PREDICTOR (Katharine Q. Seelye, New York Times) In a campaign where demographics seem to be destiny, one of the most striking factors is the segregation of voters by age. In state after state, older voters have formed a core constituency for Mrs. Clinton, who is 60, while younger voters have coalesced around Mr. Obama, who is 46. Age has been one of the most consistent indicators of how someone might vote — more than sex, more than income, more than education. Only race is a stronger predictor of voting than age, and then only if a voter is black, not if he or she is white. Age is likely to play a particularly strong role in the Democratic primary Tuesday in Pennsylvania. The outmigration of young people has left the state with the second-highest proportion of people over 65 in the country, after Florida. Fifty-eight percent of registered Democrats are older than 45, a consistent dividing line in the race.

FOUR GROUPS MAY BE KEY TO ELECTION (Gerald F. Seib, Wall Street Journal) Four groups of voters – working-class males, young people, rural and small-town Americans and Hispanics – stand out as the key pieces of that puzzle. All four groups are in flux, and they will provide the leading indicators of where the race is heading. The role of these key voting blocs will be much in evidence in Pennsylvania, a state that in many ways is a microcosm of the U.S. A surge of newly registered voters in the state likely includes a major wave of young residents; that figures to benefit Sen. Barack Obama, who has a sizable lead among younger voters in the polls. Sen. Hillary Clinton, in turn, is counting on a strong performance in the rural and small-town environs of south central Pennsylvania, where polls show her doing well. Meanwhile, working-class white males are a swing constituency in the blue-collar areas around Pittsburgh, and they have been enthusiastically courted by both candidates.