Here is an interesting article by two Politico writers that makes the case that Hillary Clinton has virtually no chance of winning the Democratic nomination. Here is a quote from that article:
Her own campaign acknowledges there is no way that she will finish ahead in pledged delegates. That means the only way she wins is if Democratic superdelegates are ready to risk a backlash of historic proportions from the party’s most reliable constituency.
Unless Clinton is able to at least win the primary popular vote — which also would take nothing less than an electoral miracle — and use that achievement to pressure superdelegates, she has only one scenario for victory. An African-American opponent and his backers would be told that, even though he won the contest with voters, the prize is going to someone else.
People who think that scenario is even remotely likely are living on another planet.
The article goes on to argue that there are several reasons why the media is pushing this theme. One is that they love a horse race. A horse race is good for the bottom line and also means that people are paying attention to their work. Another is that the media is captivated by the Clintons' ability to get out of political jams. No reporter wants to make the mistake the media made right before the New Hampshire primary.
So, assuming that her advisers understand her chances are slim, why does she keep fighting? Well, a slim chance may be better than no chance, which is what she would have if she gave up. Also, she is a competitor and doesn't want to admit defeat. There is also the fact that the next 10 races or so may actually favor her in that many of them are closed primaries where Republicans and independents can't vote.
The danger for Democrats is that Clinton will under mind Obama's chances of winning in the fall while not being able to defeat him for the nomination. Party leaders will not want that to happen. That's why, unless Obama's poll numbers go in the tank between now and the end of the primary season, superdelegates will start breaking for Obama well before the Democratic convention in August.