PITTSBURGH, PA. -- It may be do or die for Hillary Clinton. She may have to decisively win in Pennsylvania or face calls to drop out of the race.

"I am so certain that we can not only win the nomination and win the election," Clinton said.

She kicked off a frenzied day of campaigning in working class Scranton where her dad grew up and she vacationed as a child.

"We can not only have a president who not only knows where North East Pennsylvania is but has roots here,” said Clinton.

Then it was off to Pittsburgh where her husband former president Bill Clinton joined her on the stump at a rally downtown.

Clinton's banking on white, working class voters from these areas to come out in droves for her. She's behind in the delegate race and With 158 delegates on the line; Pennsylvania is the largest single prize left. And she needs to convince super delegates who may ultimately decide the nomination she's the most electable in the general election.

With so much on the line, Clinton unveiled a new campaign ad with images of Fidel Castro and Osama bin Laden.

"If you can't stand the heat get out of the kitchen. Who do you think has what it takes," Clinton asked.

Obama was quick to denounce the ad as fear mongering.

Since they last faced off six weeks ago, Obama's weathered controversies over his pastor and comments he made about bitter working class Pennsylvanians. Still, Obama's been able to close in on Clinton's once formidable lead in the state after outspending her three to one and sharpening his criticism. He now trails by seven points in a new poll.

“I've been running for president for about 15 months, and the reason I decided to get into this race despite having young kids at home, a wife who can be skeptical, was that I thought the country was really ready for a different kind of politics,” said Obama.

Obama's trying to make inroads into Clinton's base seeking out blue collar voters who he'll need in the general election if he becomes the nominee Something Clinton's hoping won't happen Tuesday.