And the winner of the Clinton-Obama slugfest ... John McCain

WASHINGTON — As a rule, presidential elections are not won or lost by what happens in April. But last week, more and more Democratic officeholders and strategists were worrying out loud about the possibility that Hillary Clinton and Barack Obama are running themselves into trouble by their unending battle for the nomination.

The negativity of the campaigning for Tuesday's Pennsylvania primary is spotlighting issues that can easily be exploited in the general election by Republican John McCain. And the increasingly personal tone of the Clinton-Obama exchanges is draining some of the enthusiasm from Democrats, who have believed for many months that 2008 would be their year for victory.

Even so, according to this month's Washington Post-ABC News poll, there is still no strong demand from grass-roots Democrats for the two senators to end their battle and turn to the challenge posed by McCain.

By a margin of 53 percent to 41 percent, those surveyed said it is more important that their favorite candidate win, even if the race goes into the summer, than that the race end as soon as possible.

Supporting that finding, by an identical margin, these Democrats said Clinton should remain in the race, even if she suffers an upset loss in Pennsylvania on Tuesday.

By contrast, my conversations Wednesday and Thursday with members of Congress and other Democratic officials found few superdelegates who are sanguine about the prospect of seeing the intraparty fight continue until the late August convention in Denver.

They were reacting in part to Wednesday night's savage ABC News debate, perhaps the nastiest since Clinton and Obama sparred in South Carolina more than two months ago.

Clinton was the aggressor in the Philadelphia tussle, frequently piling on as Charlie Gibson and George Stephanopoulos of ABC rehashed all the recent controversies that have beset Obama — and adding some new charges of their own.

It was a notably uncomfortable performance by the current front-runner, one in which he barely suppressed his irritation with the questions and delivered convoluted explanations or apologies in response.

Many of these issues clearly will be recycled by the GOP if Obama is the nominee. In potentially the most explosive, Obama's relationship with his former pastor, the Rev. Jeremiah Wright Jr., Clinton in effect gave McCain permission to go after Obama. She said Wright's words, and Obama's varying explanations of his relationship with the pastor, "raise questions in people's minds" and make this "a legitimate area" for discussion. It will take no urging for Republicans to accept her invitation.

But Clinton has her own credibility problems, and they are more severe than her opponent's. Questioned by Stephanopoulos about her fabricated story of dodging sniper fire on a trip to Bosnia, she said she was "embarrassed" by the incident and apologized again.

But that incident fed a growing skepticism about Clinton's candor. In the Post-ABC poll, just 39 percent of all voters said they now view Clinton as honest and trustworthy.

Compared to polls in 2006, she has dropped 18 points among Democrats, 13 points among independents and 7 points among Republicans.

Despite Democratic voters' willingness to see the contest continue, three times as many say the long campaign has hurt their party's chances as those who think it has helped. In increasing numbers, they characterize the race as negative, not positive, in tone. And by a large margin, they blame Clinton more than Obama for taking the campaign in that direction.

In all those respects, the Democratic politicians I interviewed are more critical of the campaign, and more worried about its effect on the party's chances, than the voters in the Post-ABC poll.

They see that, despite the big Democratic lead on the so-called generic ballot, McCain already has achieved a near statistical tie with either Obama or Clinton, trailing the former by 5 points and leading the latter by 3.

A few more nights like Wednesday, and the Democrats may find themselves lagging behind McCain. He has hardly struck a blow at them. Obama and Clinton are doing such a good job of demolishing each other, or scuttling their own chances, that McCain conceivably could coast to victory.

David S. Broder's column appears Sunday on editorial pages of The Times. His e-mail address is davidbroder@washpost.com