Clinton Must Win by a Big Margin in Pennsylvania

Hillary Clinton will likely win the Pennsylvania primary today, but for Clinton to have any chance overtake Barack Obama in the pledged delegate count or the popular vote she must win by a big margin.

After more than 40 Democratic primaries and caucuses, Obama, the Illinois senator, leads Clinton by more than 800,000 votes. Even if the New York senator wins by more than 20 percentage points tomorrow -- a landslide few experts expect -- she would still have a hard time catching him.

Clinton needs ``blowout numbers,'' says Peter Fenn, a Democratic consultant who isn't affiliated with either campaign. ``The wheels would have to come off the Obama bus, and the engine would have to blow.''

A popular-vote victory is vital to Clinton's chances because she is likely to end the primaries still trailing Obama, 46, in the race for delegates to the Democratic National Convention.

According to an unofficial tally by the Associated Press, Obama currently leads by a margin of 1,645 to 1,504 among pledged delegates and those superdelegates -- elected and party officials who get an automatic vote on the nomination -- who have indicated a preference. It will take 2,025 delegates to win the nomination.