Clinton's Delegate Math Challenge

It should come as no surprise that political science was Hillary Clinton's major at Wellesley College. But these days, she may be wishing she'd majored in math instead.

After eight straight primary losses, the New York senator is facing a mathematical quandary in the equation that would lead her to the Democratic party's nomination. She isn't expected to win upcoming contests in Wisconsin and Hawaii next Tuesday, which will further advance Sen. Barack Obama's delegate accumulation.

Her campaign is arguing she never expected to win in these states. It is counting on big wins in delegate-rich Ohio and Texas voting on March 4, and Pennsylvania voting April 22, to move her delegate count forward and stop Obama's momentum.

Clinton's Path to Nomination

While Clinton still has a viable path to the nomination, that path was further clouded Tuesday when Obama made in-roads into demographic groups once thought to be Clinton's core: women, white men, Hispanics, and low-income Democrats.

Today the Obama campaign claimed Clinton's shot at the nomination has ended.

"We believe it's next to impossible for Senator Clinton to close that pledged delegate count," Obama campaign manager David Plouffe told reporters on a conference call today.

"The only way she could do it is winning most of the rest of the contests by 25 to 30 points, and we see not a single contest on the calendar left where we would expect her to win by those margins," Plouffe said.

Disputing Obama's delegate math today, the Clinton campaign argued Obama won't have the support of enough delegates and superdelegates to sew up the nomination before the party's August convention either.

The Clinton campaign is predicting that neither campaign will get to the 2,025 delegates needed to win the nomination before the convention.

If that happens, superdelegates — those 796 party officials, members of Congress, and former Democratic presidents who can vote for any candidate they wish — could be the ultimate deciders in the nomination battle.

"No one is going to get to 2,025 without a considerable number of super delegates, " Clinton communications director Howard Wolfson told reporters today. "We are looking right now essentially at a tied contest."

"Look, our point of view is that the goal of this process is to acquire 2,025 delegates to the national convention and that at the end of the day on the floor … we will be within 25," Wolfson said.

The majority of superdelegates are sitting on the fence, but among those who have decided whom to back, Clinton leads Obama, according to ABC News' latest tallies. Obama has warned superdelegates to vote the way their home state voted.

Clinton's Tough Spot

With Obama's momentum on a roll, former George W. Bush campaign strategist Matthew Dowd says it will be very difficult now for Clinton to win the nomination.

"It's a very tough spot she's in," Dowd said. "She's in this time frame where she can't throw up a road block, there's no primary or caucus that can stop Obama's momentum in any real way until March 4 and that's a long period of time to go without winning."

Dowd said her first opportunity to change the narrative of Obama's win will be the debate in Austin, Texas, next week.

Campaigning in Texas today, Clinton said she isn't giving up.

"I want to congratulate Sen. Obama on his recent victories and tell him to meet me in Texas, we're ready," Clinton said. "This is the exciting part of the campaign. Where you really get down to saying, 'OK what are the differences, how do we draw the distinctions?'"

She told a crowd today she can hear the voices of two strong Texas women who have died — former Texas Governor Ann Richards and former Texas Rep. Barbara Jordan — urging her to go on.

"I can hear their voices saying, 'You keep going! You give the people a real choice about the future!'" Clinton said.

Going Negative

Perhaps a sign of a new, tougher, campaign strategy under new campaign manager Maggie Williams, Clinton also sharpened her attack on Obama.

"We need real results, not more rhetoric … There is a very important choice and a big difference in the candidates in this race. I am in the solutions business. My opponent is in the promises business. I think we need answers, not questions," Clinton said.

In another sign of sharp elbows, the Clinton campaign launched a negative campaign ad today in Wisconsin, where Obama delivered a policy address on the economy.

The 30-second ad questions why Obama has refused to debate Clinton in Wisconsin.

"Both Democratic candidates have been invited to a televised Wisconsin debate," the ad says. "Hillary Clinton has said yes. Barack Obama hasn't. Maybe he'd prefer to give speeches than have to answer questions."

Hitting back, Obama connected Clinton and the presumptive Republican nominee Sen. John McCain to failed leadership in Washington that he said perpetuated the economic situation.

"It's a Washington where politicians like John McCain and Hillary Clinton voted for a war in Iraq that should've never been authorized and should have never been waged – a war that is costing us thousands of precious lives and billions of dollars a week that could've been used to rebuild crumbling schools and bridges; roads and buildings; that could've been invested in job training and child care; in making health care affordable or putting college within reach," he said.

Obama is aggressively campaigning in Wisconsin until the Feb. 19 vote. The campaign is counting on a win there to further silence opponents who have suggested Obama's support comes mainly from blacks, young voters, independents and high-income, mostly male, Democrats.

"Wisconsin would be a state with a lot of working-class voters, rural voters, a large state holding a primary that you would think would be prime turf for them," Obama campaign manager David Plouffe told reporters on a conference call Tuesday.

'I Need You To Stand Up For Me'

Making no mention of her losses Tuesday night, Clinton kicked off her campaign in Texas with a rally attended by 10,000 enthusiastic supporters, many of them Latinos.

"I need you to stand up for me because, because if we stand up together, if we work together, if we fight together, we will take back America and we will make history together," Clinton told supporters in El Paso.

However, the Obama campaign argued today that in order to pull ahead, Clinton would have to win Ohio and Texas by much higher margins than she has before.

"For her to win ... she has to win blowouts," Plouffe said. "They really need to win Texas and Ohio by 20 points and we don't see any chance they're going to do that."

Clinton has only won two states by over 20 points, Arkansas and Oklahoma, Obama's campaign pointed out.

The delegate math is tricky, however, because each news organization and campaign tabulates the delegates differently. But with the proportional nature of the Democratic races — by which the delegates are allotted proportionally according to the state's popular vote — a candidate must win by a high margins to amass the most delegates.

Obama picked up another superdelegate endorsement today from the governor of Puerto Rico, Aníbal Salvador Acevedo Vilá. Puerto Rico is the last U.S. territory to vote in the primary season, on June 7, reports ABC News' Jake Tapper.

In another blow to the Clinton campaign today, former President Clinton's 1992 campaign manager endorsed Obama, touting the candidate's ability to build a coalition of Democrats, independents and Republicans going into November.

More than anything, Democrats want a nominee who can defeat the presumptive Republican nominee, Arizona Sen. John McCain, in the general election.

But if Democratic voters continue to be split on who is best to do that, the fight for the nomination appears poised to spill onto the party convention floor.

For all the enthusiasm, momentum, money and state wins that Obama has under his belt, he has yet to fully sew up the Democratic nomination.

Dowd said Clinton may be in a tough spot, but he argues the Obama campaign's strategy of trying to urge Democrats to coalesce around his campaign isn't working either.

"That's been part of their problem, they get a lead, they do well and then all of a sudden they let the story get ahead of themselves," Dowd said. "You can't really convince people you're the one if your victories haven't done it."

ABC News Kate Snow, Jake Tapper, Sunlen Miller, and Eloise Harper contributed reporting.