Voters in Pennsylvania - a state custom-made for a Hillary Rodham Clinton victory - could decide on Tuesday whether she fights on for the Democratic presidential nomination or faces mounting pressure to shut down her campaign against front-runner Barack Obama.
Obama predicted on Monday that Clinton would win the Pennsylvania primary, but said his goal is to keep it close. An Obama upset or a narrow Clinton win could be a potential knockout blow to the former first lady's presidential hopes.
The final days of the race spawned some of the nastiest campaigning by either Clinton or Obama, as they apparently sensed the balloting could be decisive in the historic race that could put the first woman or first African American in the U.S. presidency. Many Democrats fear prolonging the contest will damage the party's chances against the presumptive Republican nominee, Arizona Sen. John McCain, who effectively won his party's nomination nearly two months ago.
National polls already show McCain running about even with either Democrat despite deep voter displeasure with Republican President George W. Bush and his handling of the Iraq war and the slumping American economy.
Clinton began the Pennsylvania race with a 20-point lead in several polls, but Obama's extensive campaigning and heavy TV advertising significantly cut her lead among the state's Democrats. Pennsylvania's demographics suit Clinton. The state has a higher median age, a higher percentage of whites, a lower median household income and fewer bachelor's degrees than the country overall. These are the voters - working-class whites and voters older than 50 - who have flocked to Clinton in past contests.
Pennsylvania is the largest of the 10 primary and caucus contests remaining, with about 4 million registered Democrats and 158 delegates up for grabs in the primary. Polls were to open at 7 a.m. (1100 GMT) and close at 8 p.m. EDT (0000 GMT).
Clinton trails Obama by 139 delegates going into Tuesday's vote. Democratic Party rules for apportioning delegates to the party's national nominating convention mean that she needs to beat Obama by about 20 percentage points or more in Pennsylvania and all the contests going forward to overcome his lead - a virtual impossibility.
Regardless, Clinton aides sought to keep expectations low, insisting they would be grateful for a win no matter how close. "We really need to bear down in these last few days. The whole world is watching," the New York senator told supporters in Scranton.
Obama, meanwhile, acknowledged Clinton likely would win the state vote, but the Illinois senator told a Pittsburgh radio station "it's going to be close...we are going to do a lot better than people expect."
On the eve of the vote, the former first lady bought television time for ads that swept through modern American history - the Japanese attack on Pearl Harbor, the fall of the Berlin Wall and arch-terrorist Osama bin Laden - and declared she alone was most ready for the challenges of the White House.
The Clinton ad marked the first time a Democratic candidate in the 2008 race had resorted to images of bin Laden, the al-Qaida leader responsible for the Sept. 11 terrorist attacks in the United States. An announcer reminds voters they are choosing a candidate for "the most important job in the world."
"You need to be ready for anything, especially now, with two wars, oil prices skyrocketing and an economy in crisis. (Former President) Harry Truman said it best, `If you can't stand the heat, get out of the kitchen.' Who do you think has what it takes?" the announcer says at the end, as Clinton appears on screen. At his last event of the day, in Pittsburgh, Obama brought up Clinton's new ad and mentioned that it showed bin Laden. "That's a legitimate issue," he said. "My job as commander in chief is to keep you safe. That will be my number one task." But he added that keeping the country safe, in part, means using the military wisely and said "the war in Iraq was unwise." He was trying to draw an unnamed contrast with Clinton, whom he long has assailed for voting to authorize the use of force in Iraq. Earlier, Obama left the negative talk to aides, trying to end on a positive note after days of escalating accusations against Clinton.
Obama spokesman Bill Burton said the ad "plays the politics of fear." He claimed Clinton was to blame for allowing bin Laden to escape by supporting the Iraq war and diverting the U.S. military from pursuit of the al-Qaida boss in Afghanistan. "It's ironic that she would borrow the president's tactics in her own campaign and invoke bin Laden to score political points," Burton said.
Late Monday, the Obama campaign struck back with an ad that questioned Clinton's ability to unite the country. In it, an announcer asks: "Who has what it takes to really bring change? To finally take on the special interests - not take their money. Who made the right judgment about opposing the war and had the courage and character to speak honestly about it? And who in times of challenge will unite us - not use fear and calculation to divide us?"
Obama then appears, saying: "We are one people. All of us pledging allegiance to the Stars and Stripes. All of us defending the United States of America."
The latest Quinnipiac University Poll of Pennsylvania voters showed Clinton leading Obama 51-44 percent, an increase of 1 percentage point from a week ago. Clinton's lead is slightly larger in a Suffolk University poll, 52 percent to 42 percent. Nationally, Obama has a 7-point lead over Clinton, 49 percent to 42 percent, in the Gallup Poll tracking survey released Monday. With neither candidate able to gather the 2,025 delegates needed for nomination in the remaining contests, the party's standard bearer is likely to be decided by so-called superdelegates, the nearly 800 party officials and officeholders who can vote for either candidate regardless of state results.
Overall, including the nearly 500 superdelegates who have committed to one of the Democrats, Obama leads 1,648.5 to 1,509.5. The half delegate figures arise from Monday's report of the Democrats Abroad national convention. The organization apportions a half vote for each elected delegate or superdelegate sent to the party's August national convention in Denver. It will have a total of 11 votes. So far 6.5 are allotted to Obama, while Clinton has 3.5. Two superdelegates, each with a half vote, remain uncommitted. Meanwhile, the North Carolina Democratic Party on Monday dropped plans to host a presidential debate this weekend, citing time constraints and logistical issues. North Carolina holds its primary on May 6.
All three presidential hopefuls were trying a new venue to get their message to voters: the wrestling ring. None will appear in person, but Obama, Clinton and McCain all taped messages to air on World Wrestling Entertainment's popular "Monday Night Raw" television program on the eve of the Pennsylvania primary.