With less than 24 hours until the polls open, the Keystone State is being buried in a last-ditch onslaught of attacks from Democratic Sens. Hillary Clinton and Barack Obama as the critical Pennsylvania primary looms.

Tomorrow’s contest brings an end to a six-week primary hiatus, and with 158 delegates at stake, the Pennsylvania primary is the largest remaining for the two Democrats. North Carolina and Indiana are next up May 6.

Should Obama win the Pennsylvania primary, he would effectively sew up the nomination. But if he loses, which is likely, Clinton will almost undoubtedly soldier on, despite her slim mathematical chance of victory.

The latest average of 10 polls conducted in Pennsylvania from April 17-20 gives Clinton a lead of 5.9 percent over Obama, who has been working to narrow that gap with massive spending, even negative ads.

Obama, who raised $41 million in March alone, has heavily outspent his rival in Pennsylvania, thanks in large part to his hefty fundraising network. What’s particularly notable is his change in tone over the last few days.

The Illinois Senator, who has campaigned on messages of change and unity, acknowledged Sunday that his campaign has “elbowed back” a few times in response to criticism from Clinton, who some say is employing an increasingly-negative “kitchen sink” strategy as a last resort.

Even though he will likely lose, Obama hopes his late push will result in high turnout - especially among new voters - and at least reduce Clinton’s victory margin, making it harder for her to justify staying in the race.

Obama is expected to be in Indiana tomorrow night while Clinton’s election night “celebration” (as it’s being billed) rally will be in Philadelphia. But will there be reason to celebrate - and what kind of result will it take?

What does a “big” win for Hillary even entail? The measuring stick many use is her winning by 10 points or more. That’s at the optimistic end of the scale for the Clinton campaign, even though she was up 20 points a month ago.

Whatever the outcome of tomorrow’s primary, the process has allowed for a fascinating examination of Pennsylvania’s politics, which have maintained both practical and protectionist roots for generations.

Over the past 40 years, Pennsylvanians have leaned towards the liberal on economic issues (favoring big government) and conservative on cultural issues, leaving the state closely divided between the two parties.

The trend of the Democratic Party (at least in Bill Clinton’s tenure) has been toward more conservative economics and liberal culture. Does that leave an opening for Obama - or make his upset bid even less likely?

What’s your Pennsylvania primary prediction? Does Barack Obama have any chance of stealing this one from Hillary Clinton?