By David Brennan

Newsweek

A group of 41 former military, national security and diplomatic officials have signed an open letter calling on President Joe Biden to rejoin the Joint Comprehensive Plan of Action (JCPOA) nuclear deal with Iran, warning that failure to do so could mean a costly new war.

Biden has been clear on his desire to return to compliance with the 2015 JCPOA, which was negotiated and signed by President Barack Obama's administration—in which Biden served as vice president.

Iran has ended compliance with the deal since former President Donald Trump withdrew from the accord in 2018, and has expanded its nuclear program in retaliation to the assassinations of Major General Qassem Soleimani and scientist Mohsen Fakhrizadeh, plus new American sanctions.

Biden is demanding that Iran scale back its nuclear program before his administration eases sanctions and rejoins the JCPOA. But Tehran wants sanctions relief before it returns to the nuclear limits set by the deal.

"We strongly support restoring constraints on Iran's nuclear program by swiftly returning both Iran and the United States to the nuclear accord as a starting point for further negotiations to address the many threats posed by Iran," the letter read.

"We are clear-eyed about the threats posed by Iran to U.S. national security," the signatories continued. "The most threatening would be the development of an Iranian nuclear weapon. Preventing a nuclear-armed Iran must be the paramount objective of our Iran policy, and the Joint Comprehensive Plan of Action (JCPOA) remains the best path to achieving this objective."

Trump vowed to force Iran to negotiate a more restrictive nuclear deal, though his sanctions, diplomatic measures and military actions failed to push Tehran back to the negotiating table. Iranian leaders have celebrated what they say is their victory over Trump's "maximum pressure" campaign.

The open letter to Biden said Trump's strategy "has proved disastrous for U.S. national security," characterizing his approach as "a rejection of diplomacy and reliance on empty, belligerent rhetoric." This, they said, "has induced increased attacks against our troops and allies in the region, and increased the likelihood of conflict in the Middle East."

Trump repeatedly threatened broader military action against Iran. After assassinating Soleimani, Trump even threatened a broad bombing campaign against Iranian cultural sites, something that would constitute a war crime.

Military experts have consistently warned against a conflict with Iran, stressing such a war would result in enormous financial cost and significant American and civilian casualties.

"War with Iran would be an unmitigated disaster," the letter to Biden read. "While there is no question that the U.S. would prevail, military conflict with Iran would incur unacceptable costs to the United States and ultimately fail to advance U.S. national security."

"We must urgently reverse course, beginning by rejoining the JCPOA," the letter read. "We encourage policymakers to act quickly to bring both Iran and the United States back into compliance with the nuclear accord."

The Biden administration has tried to allay JCPOA fears by framing the accord as the foundation for a "longer and stronger" deal that would cover other issues including ballistic missiles and regional proxy forces.

Tehran has repeatedly said it is not willing to negotiate on any issues outside the purview of the original JCPOA. Moderate President Hassan Rouhani's government will have its own domestic challenges to overcome in order to return to JCPOA compliance.

Rouhani's term ends this summer when he will likely be replaced by a conservative candidate, possibly one from the Islamic Revolutionary Guard Corps. In the meantime, his government is facing a parliament dominated by conservatives—who swept last year's elections—keen to hold Rouhani and his top ministers to account.

Last month for example, Foreign Minister Javad Zarif was shouted down in parliament and accused of making overtures to the U.S., enraging conservatives who were focusing their efforts on marking the first anniversary of Soleimani's death.

David Brennan is currently a Senior Reporter for Newsweek covering world politics and current affairs. Prior to joining Newsweek in early 2018, he reported on British politics and global current affairs as a staff writer at International Business Times. He has also held reporting roles at a selection of trade publications covering the healthcare, transport and property industries. Originally from London, David graduated from the University of Cambridge in 2012 where he studied history. You can contact him at d.brennan@newsweek.com.