(CNN) -- Hillary Clinton scored a big victory in Pennsylvania on Tuesday to keep her hopes for the Democratic nomination alive. The question is whether the win came soon enough.
Barack Obama's loss in another big state and the margins by which he lost among blue-collar and rural voters on Tuesday, on the other hand, may raise questions about his electability.
Some polls had shown Clinton with a double-digit lead in Pennsylvania. But in the weeks between the last primaries in Ohio and Texas, Obama had whittled down Clinton's advantage.
Clinton's 10-point margin of victory was larger than recent polls had shown; all had her winning but some of them showed only 4 or 5 percentage points between the candidates. Watch Clinton claim victory »
But because Democratic delegates are allotted proportionally according to the vote, Clinton's Pennsylvania win does little to cut into Obama's lead among pledged delegates or his advantage in the popular vote count. Watch Obama congratulate Clinton »
The results in Pennsylvania followed trends set in previous contests: Clinton won the white vote, Obama won the black vote; Clinton won the older vote, Obama won the younger vote; Clinton won in rural areas, Obama carried the urban vote. Watch what Obama's campaign says about the results »
Look for Clinton to head into upcoming contests with the message that Obama can't win in the big states like Pennsylvania and Ohio that Democrats will need to regain the White House.
The focus is now on the next two contests on May 6: Indiana and North Carolina. Polls show Obama has a comfortable lead in North Carolina but Clinton won't give up on the state. Her husband, former President Bill Clinton, will be campaigning there on Wednesday.
It's doubtful that Clinton can overtake Obama in North Carolina; he has won all the southern states and their large black populations except for Arkansas, where Clinton was first lady when Bill Clinton was governor.
But part of the reason the Clintons will campaign in North Carolina is to make it necessary for Obama to spend more time there and away from Indiana, where polls show a tight race.
Obama needs a victory in Indiana to prove that he can win a large rust-belt state to bolster his case that he can carry the states needed to beat Sen. John McCain, the presumptive Republican nominee.
Clinton has to cut into Obama's base to gain ground. And barring a major misstep by the Obama campaign, her best chance may hinge on attacking Obama and raising doubts in voters' minds.
Clinton's challenging Obama's electability is also aimed at Democratic superdelegates, the elected officials and party leaders who are free to vote for whichever candidate they choose.
With neither candidate able to reach the 2,025 delegates needed for the nomination, those superdelegates will decide who gets the nomination. Call races for yourself and see how delegates add up »
The outcome in Pennsylvania will certainly have an impact on those superdelegates -- the pressure is on them to vote along the lines of the popular vote. But they'll also consider who has the momentum going into the general election. See how the delegate race has played out so far
Momentum will also help Clinton raise money, in which she has trailed Obama. Indeed, in the hours following her victory on Tuesday, the campaign says it raised $2.5 million.
Clinton told supporters in her victory speech that "the tide has turned." It's more like she's slowed the wave of momentum that appeared ready to carry Obama to the party's nomination.
Whether she did it soon enough is one question. Another issue: the longer the two candidates bang away at each other in the primaries, the less time there will be to repair the damage before the eventual nominee must turn his or her attention toward McCain. E-mail to a friend
CNN Political Editor Mark Preston contributed to this report.