Hillary Clinton recently compared herself to Rocky as she campaigned in Pennsylvania, citing her ability to defy the odds and pluck her presidential bid from the jaws of defeat. And indeed, Mrs Clinton will need to match every ounce of the fictional Pennsylvanian's determination if she is to stop a sequence of setbacks from finally flooring her campaign for the White House.

A string of high-profile departures from her campaign team has highlighted some significant internal disagreements. First, her chief of staff, Patti Solis Doyle, resigned in February as Mrs Clinton began to "go negative" against Barack Obama. Then a member of her finance committee had to depart after suggesting that Mr Obama's success in the race for the White House had more to do with the colour of his skin than his political ability.

Now her chief strategist, Mark Penn, has resigned after he attended a meeting in support of a free trade agreement that Mrs Clinton had opposed. But even before his "error in judgement", he was involved in damaging spats with other senior advisers over the direction of a campaign which has seen Mrs Clinton lose a huge early lead. His departure will inflict further damage.

And Mrs Clinton's current problems do not stop at internal disputes. She is losing the support of super-delegates who will, in all probability, have the final say in who represents the Democratic Party in the November election. One important super-delegate, former President Jimmy Carter, recently all but declared his support for Mr Obama.

Mrs Clinton's eagerness to win the Pennsylvania state primary on 22 April has also seen her war chest empty, with new donors harder to come by than in earlier times, when she was the clear favourite for the Democratic nomination. Mr Obama currently has twice the spending power in the state, which offers a massive 158 delegates.

All this has served to attach greater importance to Mrs Clinton's battle to win the Pennsylvania primary, a contest she has been long-since tipped to win. Defeat there, or even a less than convincing performance, could see serious pressure heaped upon her to throw in the towel. She is well capable of pulling off a significant victory, as she has enjoyed support in the bigger states during the primary contests.

But if Mrs Clinton comes away from Pennsylvania with anything other than a win, it will be harder than ever to rebuff those arguing that the only winner of a protracted battle for the Democratic nomination will be the Republican nominee John McCain. Mrs Clinton may have recovered from previous knocks, but even she will find it difficult to beat the count if she loses in Pennsylvania.