Four more years of President Trump would almost certainly kill the Iran nuclear deal — but the election of Joe Biden wouldn’t necessarily save it.The big picture: Rescuing the 2015 Joint Comprehensive Plan of Action (JCPOA) is near the top of Biden's foreign policy priority list. He says he'd re-enter the deal once Iran returns to compliance, and use it as the basis on which to negotiate a broader and longer-lasting deal with Iran.Breaking it down: Trump withdrew the U.S. from the deal in 2018, restoring U.S. sanctions and piling on new ones under a “maximum pressure” campaign that has devastated the Iranian economy.He contends that bringing Iran to its knees will eventually bring it back to the negotiating table. That has yet to happen.Iran remains a party to the JCPOA but has been systematically breaching it since last May.It's not a sprint for the bomb, but Iran has reduced its “breakout time” from one year to perhaps three months.The European signatories to the deal — France, Germany and the U.K. — have been desperately trying to save it.One European diplomat told Axios in September that he had one eye on the polls and another on the calendar, anticipating that support would arrive from Washington if the deal could only survive a few more months.But the Trump administration is attempting to finish off the deal, in part by adding a thicket of sanctions that Biden might find politically painful to remove.Rob Malley, a former Middle East adviser to Barack Obama and now president of the International Crisis Group, says those efforts will only intensify if Biden wins on Nov. 3."I’m sure there will be people around the president who’d say, 'You are the only thing that stands between a President Biden and undoing everything you did on Iran, and you now have two and a half months to do everything you can to make a return to the JCPOA impossible.'"Iran's domestic politics may prove more challenging still. The "reformist" administration of President Hassan Rouhani has been badly burned, and hardliners are expected to take over following presidential elections next June. Zarif has set a high bar for any future nuclear talks with the U.S. Photo: Iranian Presidency Handout via GettyForeign Minister Mohammad Javad Zarif says Iran will return to compliance if the U.S. does — but insists Tehran won't consider any additional U.S. demands and expects "compensation" for Trump's sanctions.Zarif expressed skepticism last month about the prospects for a follow-on agreement — even one designed only to push back the JCPOA's sunset clauses. “We spent more time negotiating those limitations than anything else," he told the Council on Foreign Relations.Where things stand: “There are obstacles — demands that Iran might make, our own politics, the more complicated relationship that the U.S. now has with Russia and China — so this is not going to be smooth sailing," Malley says.Nonetheless, he continues, “the gravitational pull is towards a return to the JCPOA."How it worksIt took Iran about six months to come into compliance with the JCPOA the first time says Ernest Moniz, the former energy secretary who played a key role in negotiating that deal.Now that "the playbook has already been run" and Iran has less to dismantle, it could be accomplished in about four months, he says. That would require help from Russia, which was critical to the 2015 process.That means the earliest Iran could return to compliance would be right around the time its next administration takes office. Moniz (L) during the 2015 talks in Vienna. Photo: Carlos Barria/AFP via Getty"A serious negotiation of JCPOA-plus probably has to wait for the new president," Moniz says, noting that new negotiations would require the approval of Supreme Leader Ayatollah Ali Khamenei.“A new president in both places is probably what is needed, at least potentially, to get the nod from the supreme leader in Iran," he says.Moniz says a revitalized JCPOA would provide the world with confidence that Iran is not building a nuclear weapons program — its original purpose — but would be insufficient.While verification measures would remain in place indefinitely, limitations on Iran's nuclear material and facilities will lapse over the next several years.A cap on Iran's supply of low-enriched uranium — "the single biggest nuclear constraint," in Moniz's view — expires in 2030.In future negotiations, Moniz adds, "regional concerns will have to be more front and center."Two paths forwardIsraeli Prime Minister Benjamin Netanyahu was one of the loudest and most influential critics of the 2015 deal.He has declined to speculate on what a potential Biden victory would mean for U.S. policy on Iran, instead staying silent and hoping for a Trump victory, Axios' Barak Ravid reports.But the Israelis, Saudis and Emiratis would oppose a return to the JCPOA, Malley says. They object to the fact that the deal doesn't constrain Iran's missiles, its proxy forces or its broader regional activities. A long way apart. Photo: Jim Bourg-Pool/Getty ImagesThe Trump administration has demanded Iran negotiate on all of those fronts as part of any deal — and claims it will be forced to if Trump is re-elected.“We are at the moment where the Iranians will recognize, because they can’t take four more years of this, they will have to enter into a negotiation," Elliott Abrams, Trump's Iran envoy, recently told CNN.What to watch: Biden envisions almost precisely the opposite path to a broader deal with Iran, but acknowledges there's no guarantee Iran will even return to compliance with the JCPOA.As with many other issues, his campaign emphasizes the need to restore America's credibility and its alliances."If Iran decides not to do it, well, I think the world would be able to address that together," Tony Blinken, Biden’s top foreign policy adviser, told the "Pod Save the World" podcast this week."And if Iran does engage in this, then at least we’d be back with the folks who helped us achieve the deal in the first place."Go deeper: Biden's allies-first approach to China