Clinton wins, but challenges remain

PHILADELPHIA (Reuters) - She's still standing.

Democrat Hillary Clinton, weeks after fighting off calls to drop out of the Democratic presidential nominating race, picked up much-needed momentum on Tuesday with a win over Barack Obama in Pennsylvania's primary election.

But the New York senator faces huge challenges if she is to wrest the nomination away from Obama, an Illinois senator who leads her in the number of delegates who determine the winner at a party convention in August.

Clinton won the state with a 10 percent point margin, adding strength to her argument that she is better placed to win big, populous states that Democrats will need in November's general election against Republican John McCain.

"It's the equivalent of a political earthquake," Pennsylvania Gov. Ed Rendell, a strong supporter of the former first lady, told shouting supporters at a victory rally.

That depends.

Clinton must use her new momentum to convince so-called superdelegates, elected officials and party leaders, that she is more likely than Obama to beat McCain.

Julian Zelizer, professor of history and public affairs at Princeton University, said Tuesday's results and accompanying "spin" or interpretation would at least give those crucial party insiders reason to pause.

"I think the numbers and margin -- combined with the spin -- will leave superdelegates wondering why can't this guy just beat her." he said. "As long as they are thinking that, she gets a little time."

CASH ON HAND

Time is not the only problem. So is money. Clinton's debt-ridden campaign trails Obama's in fundraising and cash on hand. But the campaign capitalized early on Tuesday's win, announcing some $2.5 million in fundraising in the initial hours after her victory.

What did she do right? Analysts said Clinton succeeded in securing the support from blue-collar workers, the elderly and women, while Obama benefited the most from new voters and young people.

"She's done a pretty good job of both rallying the core Democratic constituencies ... and working with the established Democratic base," said Donald Kettl, a political science professor at the University of Pennsylvania.

Nevertheless, he said Obama's weakness in those areas -- which Clinton will highlight in her argument to the party's top officials -- did not mean he could not win in November.

"He's got to be able to close the deal with those voters if he's going to be able to win in the fall," Kettl said. "(But) it's unlikely that the core Democratic constituency is going to stay home and allow John McCain to be president."

Obama, meanwhile, focused on the next contests on May 6, flying to Indiana just as the Pennsylvania polls closed.

Advisers played down his loss and said the election was fundamentally unchanged.

"If you don't think we've done well enough, ask the Clinton folks if they'd like to change places with us," Obama strategist David Axelrod said.

"We made it very clear from the beginning we didn't come in with oversized expectations," Axelrod said of Pennsylvania.

Clinton advisers said her victory would bring superdelegates to her side.

"People are going to start asking tough questions of Sen. Obama," said spokesman Mo Elleithee, pointing out her popular-vote victories in Texas and Ohio some six weeks ago.

"Why is he unable to win in these states?"

Clinton has said she would stay in the race until all of the remaining nominating contests are completed and a solution is found for Michigan and Florida, where a breach of party rules left their contests invalid.

Obama said earlier this month that Indiana might be a "tiebreaker" as Clinton was favored to win Pennsylvania and he is leading in North Carolina.

(additional reporting by Caren Bohan; editing by David Wiessler)