History may record that there were three distinct windows of opportunity for Al Gore to play a decisive role in this year’s Democratic primary contest.

The first was in the days leading up to Super Tuesday, on Feb. 5, when it seemed Barack Obama could do no wrong and a critical mass of establishment endorsements was piling up in his favor.

The second occurred this month when Florida and Michigan seemed to rule out re-votes, delivering a crushing blow to Hillary Clinton’s hopes of catching up in the popular vote.

And the third—and perhaps most irresistible—will arrive in June, after the voting is over, but before the Clinton campaign can launch a final, all-out push to make Mr. Obama the unelectable candidate.

“If Gore were to weigh in, he would have to do so before the superdelegates begin breaking for either Obama or Clinton,” said a former Gore adviser, after laying out the various scenarios that might prompt the former vice president to get involved. “The superdelegates constitute the last true contest in this race. And for many, Gore is someone they talk to, listen to, and whom a lot of them admire and respect. Having him make a closing argument for either candidate would carry significant weight with some of these last-man-standing voters.”

In the meantime: attrition. Race, gender, McCarthyism, the stained blue dress—attacks on veracity, character, readiness and electability are now the stuff of the bitter everyday exchanges between the Clinton and Obama campaigns. Superdelegates, the officials and party leaders who may ultimately select the winner, are increasingly worried that the poisonous atmosphere surrounding the Democratic primary contest will make it impossible for the party to unify around a nominee.

“If I piss on your leg, and the next day I say I didn’t really mean to piss on your leg, but if you look down and see the yellow stain, you’re going to say, ‘Come on,’” said Steven Ybarra, an uncommitted superdelegate from California. “They’re both being idiotic about this stuff.”

Of the prominent, still-uncommitted Democrats, Mr. Gore is probably in the best position to call for cessation of hostilities, if not actually to deliver a deathblow to the wounded-but-potent Clinton campaign.

Uniquely among the fraternity of failed Democratic nominees, Mr. Gore has regained his standing within the party, and then some. His early opposition to the war in Iraq and tireless advocacy for combating global warming—a cause he basically personifies—made him a liberal supernova. He won an Oscar, an Emmy, a Nobel Peace Prize. He shed his suit and tie, started dressing in black shirts and jackets and cowboy boots, and took a job with Apple. His resistance to impassioned pleas leading up to the elections in 2004 and 2008 to run again only further cemented his reputation among Democrats as the unflappable Goracle.

Mr. Gore declined, through a spokeswoman, to comment for this article.

“There is no Democrat who can dictate the nominee,” said Robert Zimmerman, a former fund-raiser close to Mr. Gore who is now supporting Mrs. Clinton. “However, Al Gore can play a unique role in uniting the party and bringing an end to the fighting after the primary and caucuses have concluded.”

“Certainly, if anybody has earned the right to do whatever he wants in political life after 2000, he certainly has earned that right,” said Alan Kessler, a former Gore fund-raiser who is supporting Mrs. Clinton for president. He added that an endorsement “might be perceived as a little bit unfair for him to do, because he is so influential.”

It is taken for granted by most Democratic insiders, with good reason, that if Mr. Gore did weigh in, it would be on the Obama side.

For one thing, he has a pained history with Mrs. Clinton, who he resented for superseding his authority in the White House. But Mr. Gore can also do math. He sees that Mrs. Clinton is trailing in pledged delegates, popular vote and states won. With her avenue to the nomination significantly narrowed, her best chance is to convince superdelegates that Mr. Obama cannot win a general election. Her final failure in this endeavor, from the perspective of an interested party luminary, might settle things. Her success assuredly wouldn’t.

“If it gets to the point where there is a real general consensus, among honest brokers of information, saying she is gaming the system—if that rises to a certain level—he may feel that he has to do something,” said one longtime Gore loyalist. “But it’s so wrapped up in his personal politics with her. He is not going to be capricious about this.”

Every one of Mr. Gore’s current and former associates interviewed for this story pointed to what they said were very real reasons for him not to get involved.

His intervention on Mr. Obama’s behalf, they say, would be seen by Clinton loyalists as a betrayal. If he acted but failed to settle things, he could cement his reputation as something of a jinx. (His endorsement of Howard Dean in 2004 was followed soon afterward by the implosion of that campaign.) And his presence in the race could overshadow the cause of Democratic reunification.

“He would think that any visible step he took to participate in the process would come with so much focus on him that it would cause a distraction,” said one.

To the extent that Mr. Gore makes his decision on that basis, one question he’ll have to weigh is whether he could possibly be more of a distraction from the party’s desired goals—presumably, to produce a nominee who can win in November—than the ongoing tug of war over a few hundred party insiders.

The Clinton campaign, after all, is basing its case at this point on the notion that Mr. Obama can’t win in a general election.

“They have been giving the electability and numbers argument,” said Alaska-based superdelegate Blake Johnson, describing the pitches he has received from the Clinton campaign.

Mr. Obama, meanwhile, is practically begging for the proceedings to be brought to a close. “He was trying to persuade me that it would be good if we all came together right now,” said Robert Rankin, an uncommitted superdelegate and California union veteran who supported John Edwards until he dropped out of the race. “To a degree, he has a point. But there are still 10 states left, and we need to hear from these people.”

Another question Mr. Gore would have to weigh is whether his endorsement would matter.

“I have known Al Gore for a long time and I have great respect for him,” said Pat Waak, the chair of the Colorado Democratic Party and an undecided superdelegate. “But I would say there are other considerations for me—each of us state party chairs have to figure out what is best for our own states.”

“Al’s done well since the election was stolen from him,” said Bob Mulholland, an undecided superdelegate from California. “But no, it wouldn’t be important to me. It might be important to other people.”

It’s all academic until Mr. Gore makes a move. And the party, for now, is still waiting for a sign.

“He enjoys the life he has, and he certainly doesn’t have to convince anybody what he is passionate about,” said Mr. Kessler. “But it’s not as though he has completely walked away from the party. It’s his party. I would look, at some point, if this thing looks like it is going to carry on till late August and to the convention, for Al Gore to step forward to sit down with the candidates and all interested parties to see if there was some way to work something out here.”