Clinton Defeats Obama in Pennsylvania Primary

With so much -- figuratively and literally -- on the line, the campaign has taken a nasty turn in recent days, with Clinton questioning Obama's readiness for office and Obama insisting that Clinton is in the pocket of lobbyists and other special interests.

The clash reached a crescendo on Monday with the release of an ad by Clinton's campaign that used images of Pearl Harbor and Osama bin-Laden to subtly raise doubts about Obama's readiness for office.

"It's the toughest job in the world," says the ad's narrator. "You need to be ready for anything -- especially now, with two wars, oil prices skyrocketing and an economy in crisis."

Obama struck back quickly with an ad of his own -- touting his own judgment in opposing the Iraq war from the start and condemning Clinton's tactics. "Who made the right judgment about opposing the war and had the courage and character to speak honestly about it?" the narrator of the Obama ad asks. "Who in times of challenge will unite us, not use fear and calculation to divide us?"

Even as the candidates warred over the airwaves, each side sought to play down expectations in advance of today's vote.

The Clinton campaign has insisted for much of the last week that Clinton's margin in the state is immaterial, focusing on the idea that a win is a win. On a conference call earlier this week, Clinton chief strategist Geoff Garin called suggestions of a 15 or even 20 point victory "ridiculous," adding: "Senator Obama made a conscious decision to try and change the stakes here. They are not spending $3 million this week simply to improve the Pennsylvania economy."

Obama has overwhelmingly outspent Clinton in the state, a function of his huge fundraising lead over the New York senator. At the end of March, Obama had $42.5 million in the bank as compared to just $9.3 million on hand for Clinton. Clinton's campaign also carried more than $10 million in debt at that time, a sign that her effort is currently running in the red.

That money disparity and Obama's leads among pledged delegates and in the raw vote make the Illinois senator's campaign confident that regardless of the results tonight he remains a strong favorite to win his party's nomination.

"Tonight's outcome is unlikely to change the dynamic of this lengthy primary," argues a memo distributed to reporters this afternoon by the Obama campaign. "We expect that by tomorrow morning, the overall structure of the race will remain unchanged -- except for the fact that there will be 158 delegates off the table."

Obama currently leads Clinton by about 140 delegates, and neither is expected to reach the required number of 2,024 in pledged delegates alone. Rather, the nomination appears likely to be decided at the convention by nearly 800 unpledged "superdelegates," a key constituency that each side is hoping to sway by their performances in Pennsylvania and ensuing nominating contests that conclude on June 3.

Polling places in the Democratic primary opened at 7 a.m. Eastern time and closed at 8 p.m.