04/23/2008 02:21 pm ET Updated May 25, 2011

Ball Is Now in Obama's Court

Read more reactions from Huffington Post bloggers to the Pennsylvania Primary results

Hillary Clinton has, as expected, won the Pennsylvania primary, matching our pre-election polling exactly by garnering a 10-point victory. Now, let the analysis begin.

Let me start with the observation that Hillary Clinton did not win Pennsylvania by running a negative campaign. The negatives that came out against Barack Obama were self-inflicted mistakes - his comment about "bitter" Pennsylvanians, his bobbling of questions over why he sometimes does not wear an American flag pin in his lapel, and lingering questions about his Chicago pastor, the Reverend Jeremiah Wright. He compounded his trouble by going negative against Clinton, because in doing so he took himself off his core message of hope, change, and the promise of a new kind of politics. He became just another politician.

And coming under the heading of "Things I Didn't Need," these multiple negative issues cropped up against him all at the same time, when he was already running in a state where the demographics were stacked against him. Pennsylvania was never realistically a winner for Obama anyway, but he may have done some damage to himself by responding the way he did. We do not yet know.

But political observers know there are ebbs and flows to every campaign and every race, and Obama is now in an ebb. However, he has shown a resiliency throughout this year, and if he can get back to his core campaign messages of hope and change, he may be able to make a full recovery.

Our polling in recent months has consistently shown that American voters want a leader who can competently manage the federal government, be an effective commander in chief, be one who can cross the aisle and unify the country, and be someone who can change the way politics is played in Washington. Obama appealed effectively to those voters earlier this year, and his challenge is to get back to that message while managing attacks from the Clinton campaign.

It would be a colossal error for the Obama campaign to respond to attacks by lashing out at the Clintons and dragging their old scandals back out into the public square. Exit polling from Pennsylvania shows that a significant percentage of Clinton supporters -- 43% -- would either vote for Republican John McCain in a general election match-up against Barack Obama, or would stay home, and Obama is not going to win those Clinton voters over to his team by bringing all the old Clinton scandals back to life. And should he win the nomination, he will desperately need those supporters.

Make no mistake -- the Clinton win in Pennsylvania puts the burden of proof back on the shoulders of Obama, who must show white ethnic voters that he is worthy of their support. He did this effectively in Wisconsin earlier this year, and he must do it again in Indiana. They were evaluating him in Pennsylvania, and he closed the gap with Clinton in the week before the election, but he was unable to close the deal with them for the reasons I mentioned above.

And his trouble winning the big primary elections could become a problem for him, particularly in the minds of super delegates who might wonder if he is too weak to win these key Midwestern states in the general election. It is certainly an argument the Clinton campaign will continue to make, bolstered by fresh evidence from Pennsylvania, and he almost certainly must win Indiana to squelch this argument against him.

And this race is bound to grow more acrimonious by the day, as open sores become festering, open wounds between the two Democratic campaigns. For Clinton, the Pennsylvania win is probably too little and probably comes too late to help. I agree with everyone else who says the mathematics just don't add up for her to win the nomination. The longer she stays in this race, the more harm is done to the party. There comes a point at which -- and I don't think we are there yet -- she begins to do real harm to her own reputation and career within the party. The question she must ask herself is, does she want that? The danger is that by the time such damage is evident to her, it could be too late.

Read more reactions from Huffington Post bloggers to the Pennsylvania Primary results