Thousands of paid workers of campaigns of presidential hopefuls, Hillary Clinton [Images] and Barack Obama [Images], spread out across Pennsylvania for house-to-house canvassing and held neighbourhood meetings and parties ahead of the crucial Democratic primary.

The candidates themselves were targeting their message to uncommitted voters for the primary, in which 155 delegates are at stake and which is considered a make-or-break exercise for the Clinton Campaign.

Besides, the state has 30 super delegates who are elected officials and party leaders and could be the deciding factor in selecting party candidate for November presidential election if both Clinton and Obama go to the party's Denver convention in August without enough pledged delegates to clinch the nomination.

The delegates will be allotted to the two candidates on the basis of percentage of votes each candidate gets. Clinton is still running ahead of Obama by a few percentage points in the state but she needs to win big to keep her presidency on firm ground.

In the final hours her campaign, Clinton continued to question the ability of Obama to take on tough issues and accuse him of running negative advertisements against her rather than dealing with real concerns of the voters.

A 30 second advertisement says, "There are more and more questions about Barack Obama. Instead of attacking, may be he should answer them."