WASHINGTON — If New Hampshire Democrats voted today, and the most recent polling is correct, the only candidates who would get any delegates at all from the first-in-the-nation primary would be Joe Biden and Bernie Sanders.

The two are not only leading the packed field of 2020 presidential contenders, but are the only contenders who have clearly separated themselves from the rest of the crowd in polling and surpassed the crucial 15 percent threshold that candidates need to hit to be awarded delegates.

Of course, the election is not today. And it may look very different when Granite State voters actually head to the polls in February.

But the dynamic between Biden and Sanders is the most important relationship in the 2020 primary at the moment.

And for all their differences, Sanders and Biden have a mutual interest in preserving their duopoly and using each other as foils. Sanders needs an establishment antagonist, while Biden, 76, may prefer running against the 77-year-old Sanders than 20 younger options.

"With Biden in the race, it gives (Sanders) someone to contrast with," said Mark Longabaugh, who was a aide in Sanders' 2016 campaign. "I still think one of Bernie Sanders' central challenges is being able to adjust to a front-runner's position and ultimately building a coalition that makes him the nominee."

Longabaugh added: "Biden has the opposite challenge. He has the ability to build a broad coalition, but his challenge is being able to consolidate really core support and enthusiasm. It seems that a lot of people are for Biden, but are they really for Biden?"

Sanders thrilled supports in 2016 as the scrappy underdog taking on Hillary Clinton. But the Vermont independent entered the 2020 contest at the top of a field that had largely adopted his worldview. Fancy fundraisers with corporate titans were out, "Medicare for All" was in.

Then along came Biden, showing little interest in kowtowing to progressive activists and holding a high-dollar fundraiser at the home of a top executive of Comcast (which owns NBC) on his very first night as a candidate.

Sanders began attacking Biden almost immediately on issues like trade, which he wielded effectively against Clinton in 2016, as his poll numbers slipped and Biden's rose.

"If you add the job loss as a result of NAFTA, which Joe voted for — Joe was a friend of mine and we're going to have this discussion in a very civil way — but Joe voted for NAFTA, he voted (for Permanent Normal Trade Relations) with China," Sanders told MSNBC's Chris Hayes. "Add those two trade policies together — you're probably talking about the loss of more than 4 million jobs."

On CNN, Sanders added, "Joe and I have very different pasts in terms of how we have voted and very different visions for the future."

Meanwhile, his campaign mentioned Biden in at least three fundraising emails to supporters, including one with a subject line, "The political and financial establishment are plotting against us."

"Bernie Sanders is trying to make this into a two-person race to recreate the 2016 campaign where Joe Biden becomes a foil for his candidacy," said Zac Petkanas, a former Clinton aide and Sanders critic.

Other Democrats think Biden stands to gain from conflict with Sanders, too.

Alan Kessler, a Philadelphia lawyer and Democratic fundraiser who attended the first Biden fundraiser, said he knows lots of party donors who worry about Sanders.

"Both from the standpoint of who's strongest to beat Trump and who's strongest to stop Bernie, it's Biden," said Kessler. "Bernie's running strong in the polls and there's a real concern that if we nominate him, we lose."

One senior Democrat, who requested anonymity to speak candidly about a subject that Biden allies would not engage in on the record, put it more bluntly: "Bernie attacking Biden is the best thing that ever happened to (Biden)" because it makes it appear that it's already narrowed to a two-person race.

Biden has so far avoided saying anything critical of Sanders, his campaign and allies note. The former vice president told a Las Vegas TV station, "The last thing the Democratic Party needs now is for there to be a fight among the Democrats that gets into something that's unseemly."

And Biden has invoked the 15 percent delegate threshold, which some Democrats saw as a signal to donors and others that the race could come down to him and Sanders.

"This field is going to be winnowed out pretty quickly," Biden told reporters in Los Angeles last week. "In order to get any delegates from congressional districts, you've got to get 15 percent of the vote. To come out of Iowa, you need 15 percent of the caucus. This is going to work it's way through relatively quickly for all of us."

Sanders allies don't disagree with that analysis.

"I think people will flirt with new exciting voices and will be hopeful for them in the future, but ultimately they will want someone who has experience and can also bring change," said Rep. Ro Khanna, D-Calif., Sanders' campaign co-chair. "I've always believed that this race would come down to Joe Biden, Bernie Sanders and Elizabeth Warren."

But Robby Mook, who was Hillary Clinton’s campaign manager in 2016, issued a warning for both Biden and Sanders, though he acknowledged it's still early.

"Right now, with so many candidates in the race, it's a luxury to have the spotlight,” Mook said in a text message. "But candidates need to be careful: You don't want the kind of knock-down, drag-out dynamic that (Howard) Dean and (Richard) Gephardt had in Iowa in 2004 that created space for John Kerry to surge up."