Who will be the real primary winner?

WASHINGTON — With neither Hillary Rodham Clinton nor Barack Obama able to secure the Democratic presidential nomination without support from the so-called superdelegates who will cast decisive votes, many dynamics are at work beyond who comes out on top in one day of balloting.

In what might seem like a paradox, the Clinton victory predicted by nearly all public-opinion polls might 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. Then again, if 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, she could call it a win.

"The margin of the vote is equally as important [as who posts the highest vote total]," said former Colorado Gov. Roy Romer, one of the nearly 800 party activists and leaders whose votes as superdelegates will put the winning nominee over the top at this summer's party convention.

About 300 of the superdelegates are still uncommitted, including Romer, who also is former chairman of the Democratic National Committee, and many of them will pore over the details of today's results to gauge how each candidate might fare in the fall and, as a result, which one deserves the nomination.

Here are some factors that will help decide whether the Pennsylvania primary is definitive:

The Spread

Clinton needs to win by at least 10 percentage points — the margin she posted over Obama in Ohio's March 4 primary — to show that she has not lost her touch in the industrial rust belt, several uncommitted superdelegates said.

If she is successful, she would be able to point out to superdelegates that she trounced Obama despite being severely outspent on television and radio advertisements in Pennsylvania, by more than a 2-to-1 ratio.

If Obama can keep the race to within 10 percentage points, or even win, he would claim that he has shown surprising strength in a state that is Clinton's demographic home turf, with many of the lower-income Democrats who have supported her in past primaries. That kind of result would give Obama momentum heading toward the May 6 contests in Indiana and North Carolina, where a sweep would make a Clinton nomination feel all the more unrealistic.

The Demographics

A loss by only a narrow margin would help Obama's contention that he had overcome the two biggest setbacks of his candidacy: the controversies over his pastor's racially explosive sermons and Obama's own remarks that economically "bitter" voters in small towns "cling" to guns, religion and anti-immigrant sentiment.

Both dust-ups threatened to upend Obama's appeal to the white, working-class voters who formed the core of Clinton's base in her Ohio victory and are seen as crucial to a Democratic victory in the fall.

Superdelegates want to see that Obama, who has struggled to extend his base beyond black voters and wealthy, educated whites, is able to compete against Republican John McCain for those swing voters in Pennsylvania and Ohio.

The Delegates

Many superdelegates will be hard-pressed to vote for Clinton if she trails Obama among the so-called "pledged delegates," those who are selected by the primaries and caucuses.

Even if Obama is thumped by double digits in Pennsylvania, Clinton would not pick up enough delegates there to cut substantially into Obama's lead. A candidate needs 2,025 to clinch the nomination.

Obama strategists said Monday that they expect to announce a series of additional endorsements by uncommitted superdelegates shortly after Pennsylvania votes. A strong showing by Obama in Pennsylvania would give superdelegates more comfort in coming forward, but a bad loss might send them back to assessment stage.