Nothing is certain about the outcome of today’s Member-vs.-Member Democratic primary in New Jersey’s 9th district — except that somebody’s not coming back to Washington, D.C., in January.

The race between Reps. Bill Pascrell and Steven Rothman is close and has consumed the fascination of the New Jersey Democrats and the two men’s allies in Congress.

“This particular race has gotten national acclaim, and it’s going to be a fight to the finish,” Bergen County Chairman Lou Stellato said. Although he is backing Rothman, he has repeatedly praised both Congressmen and said the state will lose a worthy member of the delegation.

Sources on both sides use words such as “optimistic” and “confident.” In the final weeks of the race, Federal Election Commission reports showed obvious and strange bedfellow donations from sitting Members, as they chose to get off the sidelines in what has been a painful process for Democrats.

The winner of this primary will have a safe race in the fall and a solid hold on the seat for years to come.

Pascrell has run a backslapping, aggressive ground campaign. Rothman’s team chose to spend heavily on media.

Because of the way New Jersey politics works, Rothman went into the race with a numerical advantage.

But everything changed in early May, when Pascrell played his trump card: President Bill Clinton.

Clinton has endorsed him in robocalls, his name and image have appeared in television advertising and direct mail, and the former president went to the district Friday to campaign.

The Rothman team is aware of Clinton’s effectiveness as a surrogate in Democratic primaries. Rothman spokesman Paul Swibinski said the campaign hopes to “become the first team to overcome this kind of effort from Bill Clinton.”

He also stressed that he was “excited to see Steve invited to the Oval Office.” He also said the campaign was “very appreciative” of President Barack Obama’s support, even if it fell short of an outright endorsement.

But it really is all about geography. The two men come from differing counties and will have to bring out their bases. There are three key areas: Paterson, the communities that line the Hudson River and south Bergen County.

Pascrell must pull out the vote in his hometown of Paterson in a way that defies historical patterns. It is not beyond logic for that to happen, though. Early on, when it was clear that Rothman had the demographic edge, the Pascrell camp launched a concerted campaign to register residents in his native Passaic County.

“If he turns out Paterson, he wins,” one unaligned New Jersey operative said. “If he doesn’t, he loses. It’s as easy as that.”

Rothman must do well in his stronghold along the New Jersey Palisades that overlook Manhattan.

What could make the difference, though, is south Bergen County. The area is densely populated with Irish, Italian and Polish Catholics who have a potential to swing for Pascrell, an Italian Catholic.

The party machine is so strong in New Jersey that Democratic House primaries are rare and there is little precedent to look to in gauging the race. Adding to the lack of predictability are the low expectations for turnout.

But the New Jersey operative is certain about one thing: “Wednesday’s going to be brutal.”