They are the only yardstick by which Barack Obama still trails Hillary Rodham Clinton: the 796 party insiders and elected officials, known as superdelegates, who are free to back either candidate in the race for the Democratic presidential nomination.
But if the trend of the past few days continues, Senator Obama will soon overtake Senator Clinton on this final frontier, a tipping point that could encourage a cascade of endorsements from holdouts and all but seal the nomination for the Illinois senator. Even so, some superdelegates say they are content to wait out the remaining six contests before placing their bets.
"It's another data point in a long journey," he says of the primaries Tuesday, when Obama routed Clinton in North Carolina and narrowly lost in Indiana despite one of his campaign's most difficult stretches.
The superdelegate count has come into sharp focus since Tuesday because of a mathematical milestone: the number of undeclared superdelegates – 265 – now exceeds the 217 pledged delegates up for grabs in the remaining contests.
As recently as mid-January, Clinton, with her family's deep roots in the Democratic establishment, led Obama by nearly 100 superdelegates. By Thursday morning, Obama had narrowed her lead to 13, having amassed 259 superdelegates, to Clinton's 272, according to an Associated Press tally.
Obama picked up four new superdelegates after primaries Tuesday that denied Clinton the "game changer" she had hoped would salvage her candidacy. (Clinton picked up one, Rep. Heath Shuler (D) of North Carolina, who followed through on a pledge to back the candidate who won his district.) Several new Obama backers say it is time for the Democratic Party to unite and prepare for the general election. One, Jennifer McClellan, a former Clinton superdelegate, switched allegiances after Tuesday's contests.
"Given what happened last night, it is very unlikely we will have a different result [in later contests] and it's time to come together as a party, move forward, and prepare for victory against John McCain in November," Ms. McClellan, a state lawmaker in Virginia, told reporters in a phone call Wednesday.
At least one prominent Clinton superdelegate said the primaries Tuesday raised new doubts about her candidacy.
"I want to talk to Senator Clinton. I'd like to know what her strategy is," says Sen. Dianne Feinstein (D) of California. "She's my friend and I'm loyal. On the other hand, I don't want to rend the party asunder and so I think in this one the key is really in the strategy and whether the strategy is workable."
Several Clinton superdelegates say they feel comfortable sticking with her until the last contests in June because of assurances from her aides that she would not let the nomination fight go all the way to the national convention in August.
Undecided superdelegates offer a host of reasons for waiting. Some say they want voters in every state to feel heard before weighing in. Others say a final month of hard campaigning could reveal new differences between the candidates and toughen the winner for a general election fight against Senator McCain, the presumed GOP nominee.
Some undeclared members of Congress have said the primary season has been so divisive that they fear alienating voters back home. "I have been neutral, and out of respect for my supporters, half of whom are for Senator Clinton and half of whom are for Senator Obama, I'm going to stay that way," Sen. Mary Landrieu, a Louisiana Democrat facing a tough reelection battle, told MSNBC Wednesday.
Pledged delegates – those bound by election results in their states – and superdelegates each get one vote toward the 2,025 needed for the nomination. By several reckonings, Clinton would need to win nearly 70 percent of the undecided superdelegates and nearly 70 percent of the vote in the remaining contests to overtake Obama, a very high hurdle.
Obama needs 178 more delegates for the nomination, Clinton, 329.
In a memo to superdelegates Wednesday, Obama's campaign manager, David Plouffe, argued that Obama's lead in pledged delegates and momentum with superdelegates put to rest any questions about his electability in November.
"Since the Pennsylvania primary, much of it during the challenging Rev. Wright period, we have netted 24 [superdelegates] and the Clinton campaign 17," Mr. Plouffe wrote, referring to the controversy over Obama's former pastor, the Rev. Jeremiah Wright Jr. "At some point – we would argue that time is now – this ceases to be a theoretical exercise about how superdelegates view electability."
Obama took his quest for superdelegates directly to the Capitol late Thursday morning, striding onto the House floor in the middle of a vote and chatting up uncommitted lawmakers.
Clinton vowed Wednesday to stay in the race "until there is a nominee," and pitched her case later that day to undecided superdelegates on Capitol Hill.
"Senator Obama has not proven he can win the key swing states, has not yet proven he can win the votes of blue-collar workers, and that will be the crux of the argument we make to superdelegates and voters going forward," Clinton spokesman Howard Wolfson said in a phone call with reporters.
Rep. Jane Harman (D) of California, a superdelegate for Clinton, says she is not wavering. "I think it is critically important to have a woman in a position to be president of the United States," she says. "No one has the magic number of votes yet."
Rep. Gene Taylor, a Mississippi Democrat who is uncommitted, says he sees no reason to short-circuit a race that he believes will strengthen the eventual victor. "I'm not in a big hurry," he says. "Every day they're going to be asked tough questions and every day they're going to become a better candidate or not become a better candidate."