As a White House candidate, Joe Biden said his formal plan for dealing with Iran would start with a seemingly simple first step: rejoining the 2015 Iran nuclear deal. A new nuclear crisis in the Middle East could be best averted, he argued, by keeping Tehran boxed inside the agreement’s strict, if temporary, limits, while working to negotiate stronger ones.

Yet, weeks before Biden is sworn in as president, the prospects for reviving the deal are looking more complicated. An oddly diverse collection of opponents — including close U.S. allies in the Middle East as well as Iranian hardliners and Trump administration officials wrapping up their final weeks on the job — are working to ensure that Biden’s vision is never realized.

The Obama administration’s signature foreign policy achievement has been on life support since President Trump’s unilateral withdrawal in 2018. But since the election, the deal has come under fresh assault, across multiple fronts.

The Trump administration has imposed new economic sanctions on Iran, each amounting to a fresh barrier to resuming the deal. In Tehran, conservative lawmakers sought this week to place impossible time constraints on Biden, passing legislation requiring Iran to accelerate its production of enriched uranium and kick out U.N. nuclear inspectors if sanctions on the country’s oil and banking sectors are not lifted by early February, about two weeks after Biden’s inauguration.

Most disruptive was the Nov. 27 killing by unknown hit men — widely thought to be Israeli operatives — of Mohsen Fakhrizadeh, an Iranian physicist who ran the country’s military nuclear program before it was formally disbanded in 2003. Some observers consider the assassination an attempt to sabotage the nuclear deal by making it politically harder for Iran’s leaders to return to the agreement’s restrictions, even though President Hassan Rouhani has called for a restoration of the pact.

“To restore its economy Iran needs a full or partial return to the nuclear deal. To restore deterrence [and] pride it will want to avenge Fakhrizadeh’s death,” Karim Sadjadpour, a senior fellow at the Carnegie Endowment for International Peace, said in a Twitter post. “Doing the latter without sabotaging the former is most difficult.”

The nuclear agreement — formally the Joint Comprehensive Plan of Action — was the product of years of negotiation between Iran, the United States and five other world powers: Britain, China, France Germany and Russia. In return for the ending of sanctions on Iran’s oil exports, Tehran dismantled its Arak nuclear reactor and agreed to export or eliminate the bulk of its stockpile of enriched uranium.

The pact allowed Iran to continue to make low-enriched nuclear fuel — the kind used in nuclear power plants — but only under international oversight, and with a limit of 300 kilograms, or 660 pounds, far short of what it would need to build a single nuclear weapon.

But Trump called the agreement “horrible” and faulted it for its sunset provisions — many of its limits are set to expire in 2030 — and for not addressing other issues, such as Iran’s missile production and its support for the Lebanese militia Hezbollah and the Houthis in Yemen.

After Trump abandoned the deal and imposed new sanctions, Iran began to disregard the agreement’s nuclear limits. Last month, the International Atomic Energy Agency reported that Iran’s stockpile of low-enriched uranium has swollen to nearly 8,000 pounds, about 12 times the limit set by the 2015 nuclear deal.

Biden’s key advisers have acknowledged that the effort to restore the agreement may be difficult. In January 2019, Antony Blinken, Biden’s longtime aide and his nominee for secretary of state, predicted that the nuclear deal would essentially fall apart after the U.S. withdrawal. He also told the “Intelligence Matters” podcast on CBS News that Trump’s actions would complicate or thwart future U.S. efforts to reengage.

“The one thing we got right — actually curbing Iran’s nuclear weapons program and actually putting a check on it — is the one thing we just tore up. Which makes no sense,” Blinken said. “And now it actually makes it more difficult to deal with the other challenges posed by Iran.”

Biden has acknowledged the deal’s shortcomings while blasting Trump’s exit as reckless and shortsighted.

Outlining his Iran strategy in an op-ed published by CNN in September, Biden vowed an “unshakable commitment” to preventing Iran from acquiring a nuclear weapon, while also promising to offer Tehran “a credible path back to diplomacy.”

“If Iran returns to strict compliance with the nuclear deal, the United States would rejoin the agreement as a starting point for follow-on negotiations,” Biden wrote. “With our allies, we will work to strengthen and extend the nuclear deal’s provisions, while also addressing other issues of concern.”