After Puerto Rico’s Democrats vote on June 7, there will be extraordinary pressure on the remaining publicly undecided super-delegates to get off the fence and make their preferences known. The Democratic convention is not until the end of August, so there’s a potential for three more months of Hillary Clinton and Barack Obama slugging it out, running negative ads, airing opposition research, jabbing each other in speeches, and driving up each others’ unfavorable ratings.

There are several hundred super-delegates who have not publicly committed, and even when you win the support of a super-delegate, you don’t always get to keep it. Rep. John Lewis of Georgia announced at the end of last month that because his district overwhelmingly supported Obama, he will vote for the Illinois senator if it comes to a floor fight (which looks extremely likely). And then, sometimes one of your super-delegates is forced to resign because of involvement with a prostitution ring. Some days, Hillary just can’t catch a break.

But not all super-delegates are equally influential, and the Democrats could possibly avert that protracted summer fight if, after June 7, a group of the most prominent remaining undecided superdelegates jumped on one of the bandwagons. Perhaps the lowest point of the campaign for Hillary Clinton was the rumor just before the Ohio and Texas primaries that Obama had 50 super-delegates that were ready to endorse at the end of the week. Had the boast panned out, her campaign would have been instantly rendered a Sisyphian effort to keep the final score respectable. But Hillary won Texas, won Ohio by a significant margin, and won Rhode Island — and those 50 super-delegates never materialized.

Each of the ten figures listed below has remained on the sidelines for a reason. But sooner or later, they will have to decide, and a collective endorsement from several of them could create the impression that the fight is effectively over.

The ten, in order of influence: 1. Former Vice President Al Gore. Earlier this year, there was widespread speculation — expectation, in fact — that Gore would endorse Obama, owing to lingering resentments and bad blood from his chilly relationship with Hillary during her husband’s presidency. But it hasn’t come, long after it would really do Obama some good. (A national figure like Gore really needed to make his endorsement at least one news cycle before Super Tuesday to benefit the endorsee. An endorsement today would leave Gore fans from California to Tennessee to New York lamenting, “Now you tell me!”)

The fact that Gore hasn’t endorsed may mean that reports of his antipathy to Hillary Clinton have been greatly exaggerated, or that he’s not interested in losing his less-partisan savior-of-the-planet reputation, and suddenly alienating about half the Democratic party. Gore’s endorsement ended up being the high point of the Howard Dean campaign in 2004, but this nod is likely to be more decisive than the last one, as he’s not trying to sell an untested outsider to wary Democrats (as with Dean) but simply play the role of a tiebreaker in a very close contest. 2. Former President Jimmy Carter. Carter has praised Obama — and indicated he privately criticized Bill Clinton about the latter’s comments after the South Carolina primary — but stopped short of endorsing the Illinois senator. Carter has not traditionally been a major player in Democratic presidential primaries, but as the Democratic primary gets uglier and nastier with no visible resolution, he may rethink whether neutrality really is in the best long-term interests of the party. 3. House Speaker Nancy Pelosi. Pelosi has pledged to support the delegate winner and is urging other super-delegates to do the same. In fact, she has said that the super-delegates “overturn what’s happened in the elections, it would be harmful to the Democratic party.” On paper, that would put her in Obama’s pile. But if she were to endorse Hillary before the convention, she would be offering a powerful and unspoken argument that Obama would not give the best chance to expand the Democratic majority. Similarly, coming out and endorsing Obama would be a vote of confidence, a declaration that his rough patch hasn’t damaged his ability to generate a blue wave to follow 2006.

4. Senate Majority Leader Harry Reid. Reid says he will not endorse until the convention, and with good reason, as he has to work with both senators until then (and with one or both after November). 5. Sen. Joe Biden. It would mean more for Obama if the party’s most prominent foreign-policy graybeard came out and said Obama has the capacity to be commander-in-chief. If he were to endorse Hillary, it would be less surprising, but would essentially reinforce the Obama-is-weak-on-defense theme of her campaign’s “3 A.M.” ad. (Biden issued a statement last Tuesday praising Obama’s speech on race.)

6. House Majority Leader Steny Hoyer. The Maryland congressman is telling local press that he remains undecided. Since the Democratic takeover, Hoyer has emerged as the anti-Pelosi, the voice of the less-liberal wing of the party, and those who represent purple and red districts who could be endangered by nominating the more liberal of the two contenders. (It’s debated, however, which one is more liberal.)

He appears to disagree with Pelosi’s follow-the-delegates strategy, declaring, “I think they should do what they were intended to do. Super-delegates should bring their expertise and judgment to this very critical decision on who’s going to lead our country for the next four years.”

In November, Hoyer “took particular exception to Illinois Senator Barack Obama’s assertion in a Las Vegas debate that Democratic front-runner Hillary Clinton hadn’t given ‘straight answers’ on ‘a host of issues.’ Hoyer said that comment is “likely to get used by ‘Republicans’ in the general election.” That comment was interpreted by liberal bloggers as a signal that Hoyer prefers Hillary. 7. Rep. Jim Clyburn. The giant of South Carolina Democratic politics remained neutral during his state’s primary, but expressed skepticism of the idea that super-delegates could give the nomination to the candidate who finished second in terms of regular delegates. (Clyburn noted that while he remained neutral, he did vote in the primary and thus has a favorite that he will not disclose publicly.)

The best clue to that preference is probably his effusive praise for Obama’s potential coat-tails in the south. 8. Sen. Jim Webb. Virginia governor Tim Kaine and Rep. Bobby Scott endorsed Obama, but Webb — often mentioned as an intriguing running-mate choice for Obama — has been strangely quiet. He has said that he will “not necessarily” vote for the wide-margin winner of his state’s primary, Obama. 9. Assorted red-state Democrats facing reelection. Many prominent red-state Democrats had already endorsed Obama, and Obama’s success in red-state Democratic primaries has been widely discussed. But that was before Rezko went to trial, before Jeremiah Wright came to the mainstream media’s attention, and before the candidate’s wife suggested she had not been proud of America for nearly three decades. The inspirational Obama of the night of the Iowa caucuses is gone now, and the new Obama might be as toxic in heavily conservative states and districts as Hillary. Watch Sen. Mary Landrieu of Louisiana (by far the most endangered Senate Democrat this cycle), Reps. Jim Marshall of Georgia, Nancy Boyda of Kansas, Heath Shuler of North Carolina, Brad Ellsworth of Indiana. 10. Former Gore campaign manager Donna Brazile. No super-delegate has been heard more by those watching the race closely, as she offers measured-but-blunt analysis of the race during CNN’s election coverage and on ABC’s This Week. No CNN commentator shifts in her seat as uncomfortably as Brazile when the topic turns to super-delegates, but she remains publicly neutral, and her dispassionate assessment of the race gives little clue to any conscious or subconscious preference.

However, after stating to CNN that “if 795 of my colleagues decide this election, I will quit the Democratic party. I feel very strongly about this,” it seems unthinkable that she would back the candidate trailing among regular delegates. According to most projections, she will be backing Obama after June 7.

Finally, one last voice who is not a super-delegate, but who could be very influential: John Edwards. The consistent third-place winner has been largely and strangely quiet since his departure from the race (nothing revealing on Leno last week). He’s met with Hillary and Obama, and he alternatively praised and criticized both candidates in his final weeks on the trail. His preference remains a mystery.

– Jim Geraghty writes “The Campaign Spot” blog for NRO.