Despite the momentum building behind Clinton after her win in Pennsylvania and polls showing voters drifting in her direction, it still appeared mathematically impossible for her to overcome Obama's delegate lead for the party nomination.

In the past two months, Obama has whittled Clinton's super delegate lead by half, a key gain for the Illinois senator because neither candidate can win the 2,025 delegates needed for nomination in the remaining nine state and territorial contests.

Clinton has a 20-superdelegate lead, 268-248, but Obama holds the overall advantage in delegates, including committed super delegates, 1,736.5-1,602.5.

NBC's current national delegate count stands at 1334 for Clinton and 1490 for Obama. NBC’s estimated super delegate count stands at 267 for Clinton and 248 for Obama.

[There are differences in how news organization count delegates, how they award super delegates, how they account for states that have held caucuses but have not yet chosen their delegates, and how they project the apportionment of delegates within Congressional districts where the vote was close. The Associated Press and NBC news conduct separate delegate counts.]

That means the super delegates, the nearly 800 party officials and office holders free to back either candidate regardless of state votes, will decide the nominee.

While it still may be a long shot, Clinton advisers believe she is in a stronger position to argue that uncommitted super delegates should give her candidacy another look even though she is trailing in delegates, states won and the popular vote.

Inching up

She appeared to be gaining strength among voters, especially the white working-class which has reacted negatively to Obama's association with Rev. Jeremiah Wright — the Illinois senator's former pastor who called from the pulpit for God to damn America for its treatment of African-Americans.

Clinton strategists also say that Obama's message of hope and change has worn thin as the slumping economy has diverted voters' attention. Clinton's emphasis on policy proposals, such as her plan to ease home foreclosures and her backing of a summer gas tax holiday opposed by Obama, is winning over voters, particularly the working-class backbone of the party, they say.

"There is a settled view among Democrats and in the general electorate that Sen. Clinton is the better candidate to have knowledge and leadership to turn the economy around," Clinton strategist Geoff Garin said.

A poll released Thursday by the Pew Research Center for the People & the Press showed Clinton's lead over Obama nationally among whites who did not attend college had increased from 10 points in March to 40 points at the end of April.

That voting bloc played heavily in Clinton's substantial win last week in Pennsylvania and was likely to be just as critical Tuesday, when voters cast ballots in Indiana. Pre-vote surveys there showed the outcome was a toss-up.

Slipping ratings

A second poll released Thursday carried more potential bad news for Obama, this in North Carolina, which votes the same day as Indiana. The Mason-Dixon Polling & Research Inc. survey for two television stations in the state showed Obama's double-digit lead had slipped to just seven points, 49-42.

Nationwide, the Pew poll showed, Democratic voters now are about evenly divided, with Obama holding a statistically insignificant 47-45 margin. In late March he was up 10 points, 49-39.

The latest Gallup tracking survey had Clinton leading 49-45, after a week of showing them nearly even. Obama held a 10-percentage point margin going into Pennsylvania.

The prolonged and divisive campaign was of particular concern for Democrats concerned about damage being done to the party's chances in the fall against presumptive Republican nominee Sen. John McCain.

Presumed GOP nominee

McCain on Thursday went into the heart of America's farm belt to Iowa, a place where subsidies for corn and ethanol fuel are wildly popular, to denounce agricultural subsidies.

Congress is struggling to finish a nearly $300 billion bill that McCain says is bloated with subsidies for wealthy farmers. His long-held position against subsidies has cost him in Iowa, the state that traditionally begins the presidential nominating process and is a potential swing state in the fall.

Despite his ties to U.S. President George W. Bush, whose approval rating is below 30 percent, McCain is running close to both Clinton and Obama in hypothetical matchups.

Those fears led former Democratic National Committee Chairman Joe Andrew on Thursday to switch his backing to Obama, despite having been named to the top party job by former President Bill Clinton.

"This has got to come to an end," Andrew told reporters in his hometown of Indianapolis. He said he planned to call all the other super delegates he knows and encourage them to back Obama.

Asked for a response to Andrew's decision, Clinton spokesman Phil Singer said, "We support that Democratic process and think that every American should be able to weigh in and support the candidate of his or her own choosing."

Clinton adviser Harold Ickes also sent a memo to super delegates Thursday arguing that the polls prove she is the strongest candidate to beat McCain. Among the polls they cited was an Associated Press-Ipsos survey out this week that showed Clinton leading McCain by 9 percentage points, while Obama is virtually tied with the likely Republican nominee.

This week, Obama picked up nine super delegates, plus three add-on delegates named by the Illinois Democratic Party. Clinton gained four new super delegates, while also picking up four add-on delegates from her home state of New York.

In the southwestern state of New Mexico, a group of Clinton supporters, including four New Mexico super delegates, has accused the state Democratic Party of breaking national and state party rules when it nominated a 12th super delegate.

The woman chosen has said she is undecided, but the Clinton group believes she is an Obama supporter. The Clinton supporters nominated their own candidate, who they think leans toward Clinton.