I've done some work with the delegate counts and I am coming to the conclusion that it is a virtual impossibility for Hillary Clinton to overtake Barack Obama in the pledged delegate count. Given where things stand today and if we make the following assumptions about the coming races:

60-40 Obama: South Dakota, Wyoming

55-45 Obama: Hawaii, Mississippi, Montana

50-50 toss-ups: Democrats Abroad, Guam, Indiana, North Carolina, Oregon, Puerto Rico, Rhode Island, Vermont, West Virginia, Wisconsin

55-45 Clinton: Kentucky

60-40 Clinton: Ohio, Pennsylvania, Texas

The final pledged delegate count would be:

Obama: 1724
Clinton: 1696

Obviously, this isn't rocket science and it's pretty difficult to predict some of these races (Puerto Rico for example), but I have intentionally biased this in favor of Clinton and she still doesn't come out on top.

Central to this estimate is that Hillary wins the trifecta of Ohio, Pennsylvania and Texas by 20 percentage points. She could win all three but I think her margins probably won't be that large. Remember, she won New York, her home state, by just 17 points. California she won by 10 points. Hillary hasn't scored 20+ margins anywhere except for Arkansas and Oklahoma.

If we knock Ohio, Pennsylvania and Texas down to 10-point margins the count would be:

Obama: 1752
Clinton: 1668

All of this points out the absolute necessity for Clinton to contest each and every state that's coming up. She can't afford to write off the small states as she has been doing.

There are 796 super-delegates with the breakdown currently:

Clinton: 234
Obama: 157

That leaves about 400 super-delegates still undecided. If we add the decided super-delegates to my last estimate we get:

Obama: 1909
Clinton: 1902

This means that the 400 outstanding super-delegates and the 26 Edwards delegates will decide who gets the nomination. The candidate who has won the majority of races and has the majority of pledged delegates would clearly have the upper hand in swaying these remaining delegates. The only way the numbers add up for Hillary is if she pulls off 30 point victories in Pennsylvania, Ohio and Texas. Even then she would have only a 30 delegate advantage.

Her other avenue to the nomination is if she somehow manages to sweep a bunch of the smaller states that I have listed above as 50-50 tossups. It's a tall order indeed.

Update: More bad news for Clintoniacs comes with Rasmussen's national daily tracking poll:

Obama: 49%
Clinton: 37%