Last month, President Donald Trump told Congress and United States partners in Europe that he will not extend waivers of sanctions against Iran unless they “fix” the Joint Comprehensive Plan of Action (JCPOA), a.k.a., the Iran nuclear deal.

That deal provides that previously-existing sanctions against Iran over its nuclear program be suspended, but the US Congress required the president to issue a waiver of sanctions on the Iranian oil industry every 120 days and on the country’s financial institutions every 180 days. The next oil industry waiver would be due in mid-May, and Trump’s failure to issue it would mean effectively that the US is withdrawing from the JCPOA.

To understand the consequences of such a possible decision, Columbia University’s Center on Global Energy Policy released a new commentary by Senior Research Scholar Richard Nephew exploring the issue.

Nephew begins with possible scenarios for how the oil sanctions could be reimposed, outlining the questions that would need to be answered about how long companies would be given to phase out their purchases and how broadly or narrowly the Trump administration would seek to enforce sanctions.

He then turns to international reactions, which he believes would be decidedly negative. Europe would likely register its objections and utter its recommitment to the JCPOA while taking a wait and see approach, according to Nephew.

Russia would no doubt reject the US position, and Russian firms might seek to profit from the situation, particularly if European companies were to withdraw from Iran. China, dependent on 570,000 barrels per day of imports from Iran, would also probably oppose the measure.

From an oil market perspective, Nephew estimates that somewhere in the range of 400,000 to 500,000 barrels per day would be removed. Iranian exports, in other words, would fall from 2.4 million barrels per day to 1.9 million barrels per day within a year of the reimposition of sanctions.

Nephew concludes that “the international community is largely and remarkably unprepared for a US decision to withdraw from the JCPOA.” He recommends that companies and governments take Trump’s threats seriously and “begin planning for the various contingencies they may face in May when the waivers are due for renewal.”