Clinton wins, but challenges remain

By Jeff Mason - Analysis

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.