Although Obama's lead appears almost insurmountable, relatively few delegates separate the two candidates, and their popular-vote percentage differences are even smaller. The remaining string of primaries could prove inconclusive.
Hoping for a miracle, and a major Obama mistake - and fearing that this might be her only chance to be president - Clinton might soldier on, knowing that she enjoys strong support among many party voters. Far more hopeless campaigns then hers went all the way to the convention without conceding. Why should she?
And under what imaginable circumstances would front-runner Obama concede? Should a superdelegate cabal decide to swing the nomination to Clinton, the reaction from Obama supporters would be fierce.
It's time for more than wishful thinking. It's time for the party's leadership to act. The best way to bring this bitter nomination battle to a close in a way that is thoroughly fair and absolutely decisive is to move the convention date from late August to late June.
Moving up the convention to June 28-July 1 would allow fair competition for each candidate in the remaining primaries, while avoiding a summer-long battle for holdout delegates. As an added bonus, it allows the Democrats to end with a patriotic flourish just before the Fourth of July.
Moving up the convention date also would do more than simply advance the day of decision: It would force the issue of choosing the nominee in a way nothing else can. The 300 or so remaining superdelegates would have no choice but to get off the fence - and to do so soon. A late June convention could mean a decision by late May, or sooner.
Settling the issue at the actual convention would endow the nomination with maximum legitimacy. Tennessee Gov. Phil Breseden has suggested a miniconvention of superdelegates. While logistically easier, this idea is politically treacherous, perhaps guaranteeing that the loser would claim that the nomination had been stolen by party elites. Only a full convention with all delegates present - both elected and super - would have the legitimacy the party now desperately needs to rebuild the unity to take on McCain.
Moving such a large convention in time would surely be a logistic nightmare, not to mention a sharp break with tradition. But there is good news. The Pepsi Center, the site of the Democratic Convention, is free on June 28-July 1, and the Democratic National Committee has actually already booked it for several days in early July. Any remaining logistic problems, important as they would be, must be weighed against the real possibility of hopelessly dividing the party and losing the presidency. The front-loading of the primary calendar has already made a late August convention completely anachronistic. The closeness and bitterness of this campaign has hung the albatross of this year's utterly irrational primary and convention calendar right around the party's neck.
Meanwhile, as the Democrats spend fortunes defining each other, the so-called Straight Talk Express of John McCain rumbles along.
"Who is John McCain?" it asks.
He's that genuine American war hero turned political "maverick" who tells you just what he thinks. And what is that? How willing he is to reprise classic Republican dirty tricks, such as lying about his Democratic opponents by claiming they want to wave the "white flag" of surrender to al-Qaida in Iraq?
The times have changed. The primary calendar this year is like none other before.
For many years now, the great majority of the delegates have been chosen by the voters. But the date of the convention is just where it's always been, months after the last polls close.
It's time for the Democratic National Committee and party chair Howard Dean to show real leadership.
Move the convention to the end of June and put the party in the best position to end the tragic foreign and domestic legacy of President George W. Bush.
Tom De Luca, professor of political science at Fordham University, is co-author of "Liars! Cheaters! Evildoers! Demonization and the End of Civil Debate in American Politics." He blogs at dailydemonizer.blogspot.com