First let's begin with a quote from Clinton supporter Charles Rangel of New York.

"If mathematically she couldn't get the nomination, it would mean that Obama has won and so she wouldn't be in the race," said Rangel. "And so obviously mathematically she can." When asked how she could win the nomination, Rangel replied, "I don't know, but if mathematically she cannot win, then why aren't we declaring Obama the winner? I mean, it doesn't make sense. It is not my job to explain how, if she put $6 million of her money, the team is still together, the campaign is still going on, why do I have to explain mathematically why she can't win? If mathematically she can't win, then they are crazy. They ought to go to an insane asylum." He added, "Anybody who really knows that they can't win and they won't quit, there is really something wrong with them."

Here are reasons why it is so mathematically difficult for Clinton right now.

The first reason is that Obama exceeded popular vote expectations when he came within less than 2% of the popular vote in Indiana and double digits in North Carolina.

My original popular vote forecast—which stemmed from projections of the final eight Democratic primaries—credited Obama with a 156,000-vote combined plurality from Indiana and North Carolina. That was based on a somewhat conservative estimate of his support in both states. (I had him winning North Carolina by 12 and losing Indiana by six, but he actually won Carolina by 14 and lost Indiana by just two.) So his net popular-vote gain on the day was actually around 210,000. That’s no small difference with so few contests remaining.

http://origin.observer.com/...

The next reason is the expected voter turnout may not yield the necessary dividends to overturn Obama's lead in the popular vote.

West Virginia (May 13)<</p>

Turnout estimate: 475,000
The primary is open to Democrats and, for the first time, independents.
Clinton: 65% (308,750)
Obama: 35% (166,250)

Kentucky (May 20)

Turnout estimate: 570,000
Rationale: Only registered Democrats are eligible to participate.
Clinton: 65% (370,500)
Obama: 35% (199,500)

Oregon (May 20)

Turnout estimate: 655,000
Rationale: The turnout figure would be much higher, but the primary is closed, and only registered Democrats are eligible.

Obama: 57% (373,350)
Clinton 43% (281,650

)

Puerto Rico (June 1)

Turnout estimate: 700,000
Rationale: Manuel Alvarez-Rivera’s guess was 600,000, but since this is a Clinton state and these estimates are designed to give Clinton the benefit of the doubt, we’ll go with his high-end projection of 700,000.

Clinton: 60% (420,000)
Obama: 40% (280,000)

Montana (June 1)

Turnout estimate: 210,000
Rationale: Turnout was 37 percent the last time around, so we’ll bump it up to 50 percent for what will be the state’s first consequential presidential primary in decades.

Obama 61% (128,100)
Clinton 39% (81,900)

South Dakota

Turnout estimate: 90,000
Rationale: Why the big drop in turnout from Montana? Because South Dakota is a closed primary state. There are about 200,000 registered Democrats in the state, and we’ll go with 45 percent turnout (again, trying to err on Clinton’s side here, since this should be Obama country).
Obama: 61% (54,900)
Clinton: 39% (35,100

Based on these projections, Clinton would increase in popular vote by about 300,000 votes, but Obama is ahead of Clinton by 414,278, not including caucus election numbers. Even if Michigan and Florida are added and Obama receives the uncommitted votes in Michigan, he still would be ahead by 140,000 votes. Thus, the only way Clinton can win the popular vote is for the turnout in the above states to be higher than projected or win with a higher margin than projected. She can also argue that Obama should not be credited with any Michigan votes since he took his name off of the ballot. http://origin.observer.com/...

When asked how she could win the nomination, Rangel replied, "I don't know, but if mathematically she cannot win, then why aren't we declaring Obama the winner? I mean, it doesn't make sense.