President-elect Joe Biden is still committed to re-enter the Iran nuclear deal and follow-up negotiations if Tehran returned to "strict compliance", he told The New York Times on Tuesday.
But the Biden administration will have to deal with new complications that have emerged since President Donald Trump withdrew from the accord in 2018.
"A lot of things have happened since 2018 when Mr Trump left the agreement that, if not negotiated, at least have to be addressed," Kenneth Katzman, an Iran specialist at the Congressional Research Service, told The National.
“Normally, this would presumably need to be spelt out in terms of commitments that the United States needs to make and additional Iranian commitments in terms of the new facilities, and maybe new activities that they have done since they stopped complying in 2019.”
Since Mr Trump’s withdrawal, Iran has started to breach key provisions of the deal, stockpiling 12 times the amount of low-enriched uranium permissible and testing advanced centrifuges barred by the agreement.
Iran has also started rebuilding its Natanz uranium enrichment centre after a fire in July, which Tehran has attributed to sabotage.
The International Atomic Energy Agency, which still has access to Iranian nuclear sites as outlined under the deal, has not said that rebuilding Natanz breaches the nuclear pact.
But it represents one more issue the Biden administration will have to iron out with Iran, even as it sorts through the hundreds of sanctions the Trump administration has placed on Tehran.
Those sanctions go beyond those that existed before the deal, which was signed under the administration of Barack Obama in 2015.
And Iran hawks in the departing Trump administration are hoping to place even more sanctions on Tehran in their last few weeks in power as part of an "Iran sanctions wall" meant to complicate Mr Biden's efforts to revive the deal.
Mr Biden could remove many of these additional penalties at once using the same national security waiver used by Mr Obama and by Mr Trump before his 2018 withdrawal to provide the sanctions relief to which the US had committed to under the deal.
But as Mr Katzman noted: “You’re talking about hundreds and hundreds of entities that would need to be delisted.
"Iran didn’t take too kindly to the IRGC [Islamic Revolutionary Guard Corps] being named a foreign terrorist organisation.”
Even if Iran allowed Mr Biden to keep Mr Trump's 2019 terrorist designation on the IRGC and his November sanctions on supreme leader Ayatollah Ali Khamenei's personal foundation, other sanctions present thornier issues.
“I’m pretty sure they would demand that the Central Bank no longer be designated as a terrorism entity,” Mr Katzman said.
Although the US Treasury Department formally maintains an exemption on humanitarian trade with Tehran, Mr Trump’s October sanctions on the country’s Central Bank sought to cut Tehran off from the global financial system.
That exacerbated its currency crisis and discouraged companies from medical and agricultural trade with Iran as Covid-19 ravages the country.
Iranian President Hassan Rouhani and Foreign Minister Javad Zarif have indicated that they are receptive to reviving the deal.
But it could take months for Iran to rid itself of the excess low-enriched uranium and dismantle the advanced centrifuges to return to compliance with the accord.
That would mean US sanctions would remain in place, even at the start of the Biden administration.
The nuclear deal has already become a political football between Iran's hardliners and the moderate and reformist camps before the presidential elections, set for June.
The assassination last week of Iran's top nuclear scientist Mohsen Fakhrizadeh, an act Iran blames on Israel, has prompted Iranian hardliners to push harder on the nuclear issue.
The Iranian Parliament passed a bill this week that would require the Rouhani government to ban International Atomic Energy Agency inspections and resume uranium enrichment to 20 per cent.
But the legislation is largely symbolic as supreme leader Mr Khamenei has the final say on matters related to the nuclear programme.
All together, this makes Mr Biden’s pledge to negotiate a follow-on agreement especially ambitious.
"In consultation with our allies and partners, we're going to engage in negotiations and follow-on agreements to tighten and lengthen Iran's nuclear constraints, as well as address the missile programme," Mr Biden told The New York Times.
Mr Katzman said Iran might be willing to make some concessions on extending the deal’s sunset provisions and on its ballistic missile programme, but not on its regional proxies in Iraq, Syria, Lebanon and Yemen.
“Iran has categorically rejected any discussion of limitations on its regional interventions,” Mr Katzman said.
“Iran’s view is that they did not start a lot of the conflicts, and Iran is involved at the request of certain parties.
"Iran’s view is that everyone else is meddling in these conflicts, everyone’s intervened in these conflicts, and they are not going to be held to some limitations when everyone else is free to intervene.”
Regional conflicts aside, Mr Katzman said it was conceivable that Iran could agree to codify its ballistic missile range of 2,000 kilometres in a new agreement.
And while the UN arms embargo on Iran expired in October as the nuclear deal’s first sunset provision, the first restrictions on Iran’s centrifuges do not expire until 2025.
“Reading between the tea leaves, my sense is that they would be willing to entertain extending some of the deadlines,” Mr Katzman said.