Asked this week if she would carry on battling for the Democratic nomination all the way to the Denver convention in August, Hillary Clinton hinted that her uphill march may yet be halted before it reaches the Rocky Mountain destination.

“Well, I’m going until we get Florida and Michigan resolved,” she said. “I’m going until everybody’s had a chance to vote in this process. I’m going until the automatic delegates have made their judgments.” Although underlining her determination to explore every possible route to victory – no matter how narrow – Mrs Clinton’s answer also indicates that there are at least three different points in her journey to Denver when the “road closed” signs could appear.

Before the result from the Pennsylvania primary, Barack Obama led Mrs Clinton by 1,650 to 1,508 delegates and she desperately needs her uncontested “victories” in Florida and Michigan to count if she is going to begin closing this gap.

Both these states had their delegates barred from the convention because they broke party rules by holding primaries ahead of schedule in January. Attempts to broker a settlement have so far run into the sand – and this is where they are likely to remain unless Mrs Clinton manages to put real pressure on the Democratic leadership to change its mind.

For that to happen she needs to raise real question marks about Mr Obama’s electability by putting together a string of victories in most of the remaining nine contests.

The next key date is May 6. Mr Obama is the strong favourite to win North Carolina, which votes on that day, while the other primary in Indiana is shown by polls as too close to call. Significantly, Mr Obama chose to hold his Pennsylvania primary party in Indiana which, he says, “may end up being the tie-breaker”.

Should Mrs Clinton win – and avoid being wiped out in North Carolina – she would earn the right to carry on towards potentially more fertile ground in West Virginia the following week, Kentucky on May 20 and Puerto Rico on June 1. Other states still to vote, including Oregon, Montana and South Dakota, are regarded as natural territory for Mr Obama.

If she loses Indiana, a large number of the remaining uncommitted automatic – or “super” – delegates are expected to support Mr Obama and the race will be effectively over.

The Democratic elite of 795 super-delegates comprises elected officials, members of Congress and the otherwise great and/or good of the party. Both campaigns accept that these delegates will prove decisive in determining the outcome of this finely balanced contest.

Today Mrs Clinton held a much reduced lead of 23 over Mr Obama among this group. If she is to overtake her rival in the overall count, the remaining 300 or so super-delegates still up for grabs would have to to back her by a ratio of two to one.

In the past two months the tide has been almost entirely in the opposite direction with Mr Obama picking up 100 super-delegates to Mrs Clinton’s net total of only nine.

Mr Obama’s campaign emphasises repeatedly the remorseless mathematical logic that, barring “tragedy or travesty”, points to him being the nominee. He has five times more cash on hand to spend on the coming contests than Mrs Clinton and there is a growing sense of exhaustion among Democrats who just want this once-exciting but now damaging race to be over.

But the reluctance of hundreds of other super-delegates to declare for him just yet reflects nagging doubts about whether he can win in November against John McCain, as well as residual loyalty to the Clinton brand.

Howard Dean, the chairman of the Democratic National Committee, wants super-delegates to make up their minds by July 1, leaving the party with almost two months to heal its wounds before the convention in August. This still gives Mrs Clinton time to find a good argument for why super-delegates should risk accusations of overturning the will of voters in primaries and caucuses.

Her campaign has already been rehearsing some contentious lines ahead of the Pennsylvania result suggesting that Mr Obama risks alienating the white working class whose votes the Democratic party will need to win in November’s general election against John McCain.

“The Obama campaign has simply not done a very effective job connecting with blue-collar and middle-in-come voters, and they are the heart and soul of the Democratic Party,” said Geoff Garin, Mrs Clinton’s chief strategist. He added that Mr Obama’s “appeal among white voters typically has been among the people who are the most affluent”.

Mrs Clinton’s best chance is to overtake Mr Obama in the popular vote. On most counts, she trails Mr Obama currently by more than 700,000. This lead is shortened significantly if Florida and Michigan are included. The gap could be closed all together if she can hang on until the “second-class citizens” of Puerto Rico – who are barred from voting in the general election – have their Democratic primary. Over a million are expected to turn out in a contest where her advantages among Latino voters and role representing hundreds of thousands of Puerto Ricans as New York senator should give her a handsome victory.

It would almost be fitting if a group of voters whose relationship with America is riven with uncertainty were to throw fresh doubt over the outcome of a race for the presidential nomination in a party that really cannot make up its mind.

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