It was in the end a famous victory for Hillary Clinton. She won it in the clapboard row-houses of white, working-class communities, among religious, gun-loving rural types. She even won in the affluent exurbs of Philadelphia where voters flirted with Barack Obama, only to dump him at the last minute.

As the results of Tuesday's vote came in, Mrs Clinton and her exuberant supporters, including the black Mayor of Philadelphia, Michael Nutter, were packed into the Bellevue, a century-old ballroom in downtown Philadelphia.

It was an odd place to celebrate a comeback victory as the Bellevue is notoriously the scene of the world's first outbreak of deadly legionnaires' disease. Back in 1976, members of an American Legion convention were struck by mysterious bacteria, which killed 34 of them.

Thanks to Mrs Clinton, an equally deadly affliction has struck the Democratic Party, one that could deny it the keys to the White House for the third successive time in November. Mrs Clinton beat Mr Obama by a wide enough margin to justify staying in the race. That means that the death spiral the candidates are locked into continues. Just when the Democrats need to unite against the popular Republican presidential candidate, John McCain, they are locked in an unending civil war.

Inside the Bellevue, Mrs Clinton's exuberant supporters waved banners and cheered. One young man wore boxing gloves and punched the air, Rocky-style, invoking the gritty fighting style Mrs Clinton is become famous for. In her speech Mrs Clinton used the words "fight", "fighter" and "fighting", signalling that she has no intention of being bullied out a contest even if she remains incapable of winning it without ripping the party apart.

Amid some of the most negative campaigning seen in the primary contests, Mrs Clinton won through a powerful coalition of women, white voters, the working class and the elderly right across the state. Only in Philadelphia did Mr Obama do well, where he won two-thirds of the largely African-American vote. Even this win was blunted by Mrs Clinton's ally, Mayor Nutter, another charismatic star of the Democratic Party.

Mrs Clinton started the campaign with a huge advantage of name recognition. Pennsylvania, the birthplace of her father and place her family holidayed, is something of a second home for Mrs Clinton. Pennsylvanians, unlike many Americans, tend not to move far from where they were born and loyalty and family ties are powerful forces here.

The young, mobile well educated Americans, who elsewhere flocked to Mr Obama's promise to renew America's politics, were out-gunned by Mrs Clinton's more conservative supporters. And in a grinding campaign that lasted six long weeks, the spell Mr Obama managed to cast over voters in other states with his inspirational message of bringing change to Washington came across as stale and unconvincing.

He also battled against the worst controversy of his campaign, when the incendiary words of his former pastor, Jeremiah Wright, in a sermon were broadcast again and again on television. Mr Obama also came across to Pennsylvania's voters as another conventional politician rather than the wunderkind who persuaded the predominantly white state of Iowa to back him back in January.

Mrs Clinton ruthlessly exploited private comments he made saying the people of smalltown Pennsylvania were not supporting him because they were "bitter" about their lot in life and "clinging" to guns and God in response to economic hard times. And in final dying days of the campaign she invoked the image of Osama Bin Laden in an ad to make her point that Mr Obama is not ready to defend the country.

Even as people turned out to vote, Mrs Clinton took a leaf out of George Bush's political playbook to use fear of terrorism to sway voters, adding that as President she would "obliterate" Iran if it threatened to attack Israel. It did the trick and Mrs Clinton won handsomely among the poor, ill-educated voters who get their news from morning television.

Now the danger for the Democratic Party is that the longer the struggle goes on, the more disenchanted each candidate's supporters will be when a candidate finally emerges.