Iran’s recent rebuff of President Joe Biden’s offer to commence talks on getting both Washington and Tehran back into compliance with the Iran nuclear deal has, at least temporarily, thrown a monkey wrench into Biden’s strategy for quickly reversing Iran’s relentless march away from the restrictions of the 2015 agreement, formally known as the Joint Comprehensive Plan of Action (JCPOA). While efforts to get Iran to the negotiating table will no doubt continue in the coming days and weeks, it’s long past time for the United States to start thinking seriously about what it will do to contain Iran’s expanding nuclear program in the meantime. While it waits for serious talks to begin, much less succeed, how long is the United States prepared to simply stand by and watch as Iran continues, month after month, to ratchet up its nuclear activities, inching ever closer to some kind of threshold nuclear weapons capability?

In response to the Trump administration’s withdrawal from the JCPOA and reimposition of draconian sanctions, Iran has been engaged since the summer of 2019 in a steady, sustained campaign to violate the JCPOA’s constraints. Taken individually, each breach can appear incremental and not overly concerning. But taken together, cumulatively, they paint an increasingly alarming picture.

As detailed in a recent report by the Institute for Science and International Security, Iran’s stockpile of low-enriched uranium (below five percent concentration of uranium-235) is now fourteen times greater than the JCPOA’s limits. If further enriched closer to 90 percent purity, that might already be enough for up to three nuclear bombs. Iran’s breakout estimate—defined as the time required to enrich enough weapons-grade uranium for its first nuclear device—has dropped from one year under the JCPOA to potentially as low as 2.7 months today. The material for a small arsenal of three bombs could possibly be produced in as little as six months.

The danger has dramatically intensified more recently. For more than a year, Iran has been enriching uranium to 4.5 percent, breaching the nuclear deal’s limits of 3.67 percent. But beginning in early January, it took a qualitative leap forward by resuming enrichment to 20 percent at Fordow, a facility built deep inside a mountain that Iran kept hidden from the world until it was exposed by the United States in 2009, and where the JCPOA had banned all enrichment until 2030. As a technical matter, enriching uranium to 20 percent represents 90 percent of the work required to produce weapons-grade material.

Iran is also significantly increasing its enrichment capacity. For months, it’s been conducting research and development on up to nine different models of advanced centrifuges and in numbers that far exceed the JCPOA’s limits—gaining new knowledge and expertise, it should be stressed, that no return to the JCPOA can now reverse. Perhaps more worryingly, Iran has recently begun to deploy hundreds of these advanced centrifuges in cascades at its two main enrichment facilities, Natanz and Fordow. Some are already operational. These second and third-generation centrifuges are anywhere from three to seven times more efficient than the older models permitted under the JCPOA, allowing them to produce far larger quantities of enriched uranium in a much shorter timeframe. Once their installation is complete, Iran’s enrichment capacity will be almost three times larger than the JCPOA’s cap.

Another hugely provocative step recently taken by Iran, again in flagrant violation of the JCPOA, was its decision to begin producing uranium metal—one of whose uses can be forming the core of a nuclear weapon. The United Kingdom, France, and Germany, the JCPOA’s European participants known as the EU-3, said they were “deeply concerned” since the move had “no credible civilian use” and carried “potentially grave military implications.” Already gaining important knowledge by producing small quantities of metal in research and development work, Iran has declared a multi-month plan to install equipment for potential use in the large-scale production of enriched uranium metal, which it claims will be used for reactor fuel.

Also of profound concern were steps Iran took in February to drastically curtail inspections by the International Atomic Energy Agency (IAEA). A far more acute crisis was averted only when Rafael Grossi, the agency’s director-general, rushed to Tehran to negotiate a last-minute understanding that, at least temporarily, averted a situation that in his words “would not have been reversible or recoverable” in terms of non-proliferation, and where the IAEA “would basically be flying blind without any idea what would be taking place in terms of enrichment activities”. Grossi said that the arrangement gave the IAEA “the minimum that it needs” to conduct necessary verification and monitoring activities, but only for a period of up to three months and only if, in the interim, the United States grants large-scale sanctions relief to Iran. If that doesn’t happen, Grossi acknowledged, Iran at the end of the three months is threatening to destroy critical monitoring data being gathered through technical means on its nuclear activities, rather than providing the information to inspectors.

The IAEA is also in a significant conflict with Iran over several sites that were once linked to Iran’s secret nuclear weapons program. In violation of Iran’s obligations under the Nuclear Non-Proliferation Treaty (NPT), none of the sites were ever declared to the IAEA. All of them have subsequently been razed and sanitized as part of a massive concealment effort. Much information about the sites only became known as the result of an archive of nuclear weapons documentation that Israeli intelligence miraculously spirited out of Tehran in 2018. After much Iranian stonewalling, the IAEA gained access to four of the sites over the course of 2019 and 2020 and found evidence of man-made uranium particles at three of them. Pressed to explain why, Iran’s answers to the IAEA have so far ranged from “not technically credible” to unresponsive. The bottom line: in addition to the alarming expansion in Iran’s declared nuclear program, there is now strong reason to suspect that Iran is concealing from the world undeclared nuclear material once linked to its clandestine nuclear weapons effort. What happened to that material?

Finally, as if tensions surrounding its accelerating nuclear escalation were not already high enough, the Iranian regime has recently thrown in some extremely worrisome rhetorical flourishes as well. Supreme Leader Ali Khamenei warned last month that, if judged necessary, Iran might next move to 60 percent enrichment. And that shot across the bow was preceded by Iran’s intelligence minister dropping a hint that if Iran was pushed too hard, it might eventually decide to develop nuclear weapons—despite repeated claims that a fatwa, or binding religious decree, issued by Khamenei had forever banned the Islamic Republic from doing so.

Put it all together and it’s clear that the situation is getting very dangerous. And there’s a strong chance that it will get worse still. For its part, the Biden administration hoped it would be able to stem the brewing crisis by rapidly negotiating a return to the JCPOA. That clearly hasn’t happened—at least not yet. But even if a negotiation gets going, it’s increasingly clear that it will likely be a much more complicated, messy, and drawn-out process than many JCPOA supporters anticipated. So, the question emerges: What does the United States do while waiting for a return to the JCPOA? How much further is it prepared to let the Iranians go in pushing the nuclear envelope? How much nuclear expansion is too much?

Of course, it should be underscored that the vast majority of Iran’s JCPOA violations occurred during Donald Trump’s final nineteen months in office, including the move to 20 percent enrichment. Trump threatened upon abandoning the JCPOA in 2018 that Iran “would face very severe consequences” if it responded by restarting its nuclear program. But when Iran actually called his bluff, repeatedly, Trump did precious little about it. The only tool in his kit bag were unilateral sanctions and when a barrage of designations unprecedented in U.S. history—around 1,000 Iranian entities were ultimately targeted during Trump’s single term—did nothing to slow the methodical growth of Iran’s enrichment efforts, the administration had no answer, no plan B.

In retrospect, it was a stunning act of diplomatic malpractice in the face of a contingency that was entirely foreseeable, even probable, from the minute Washington withdrew from the JCPOA. By the time Trump realized after his electoral defeat what he’d wrought, and queried advisors over whether a military strike to stem Iran’s nuclear advancement was still feasible, he was allegedly disabused of the idea by warnings that an attack could trigger a major war in the final weeks of his presidency. Instead, Trump opted to leave his successor with an Iranian nuclear program that was many times larger and significantly more dangerous than the one he inherited in 2017.

For its part, Israel had a far more serious approach to the alarming uptick in Iran’s nuclear activities. Not only did its intelligence services pilfer the nuclear archive, but they allegedly were also the hand behind the audacious destruction last July of an above-ground factory for the mass assembly of advanced centrifuges, as well as the assassination of the scientific mastermind behind Iran’s nuclear weapons program in November. But all to very uncertain effect. Indeed, Iran is now rapidly building a new centrifuge factory, this time deep inside a mountain, while the assassination triggered Iran’s parliament to pass a law that actually accelerated the regime’s JCPOA violations.