President Trump ditched two key members of his foreign policy team in the span of two weeks, and perhaps no international agenda item is now set to undergo as big a change as the U.S. posture on the Iran nuclear deal. Outgoing Secretary of State Rex Tillerson and national security adviser H.R. McMaster have been holding Trump back from withdrawing from the agreement; their replacements, current CIA Director Mike Pompeo and former U.N. ambassador John Bolton, respectively, have pushed to leave it.

That makes a U.S. pullout from the deal more likely, particularly when you consider that Trump explicitly mentioned differences with Tillerson over Iran in his decision to remove him. In short, the guardrails have come off. There remain only two Cabinet-level officials who are known to be advocating for remaining in the agreement: James Mattis, the secretary of defense, and Dan Coats, the director of national intelligence.

Trump had already opened up the possibility of a U.S. withdrawal from the Iran nuclear deal when in January he set a May 12 deadline for Europe to come up with fixes to strengthen the agreement, which Germany, Great Britain and France (as well as Russia and China) are also parties to. If they don’t, Trump has vowed to let nuclear-related sanctions snap back into place — reneging on a U.S. commitment and robbing Iran of its primary reason for staying in the agreement.

Europe and Iran both appear to be bracing for a U.S. withdrawal in the wake of these staff changes. But what would that withdrawal look like? And what could happen next? Bolton has called for military action against Iran. But there are still many forms that a withdrawal from the deal could take, and Bolton isn’t the only one with input.

Here are the four main approaches to withdrawal, from least to most aggressive, that Trump could take on the deal after the May deadline passes — and what they could mean for the day after.

1. Trump reimposes a limited number of sanctions

When six world powers agreed in 2015 to lift sanctions on Iran in exchange for curbs on Tehran’s nuclear program, they rolled back a historically restrictive collective financial pressure campaign targeted at Iranian organizations and people responsible for the country’s nuclear work. Before the deal was reached, throughout the 2009-13 nuclear crisis, the U.S. also unilaterally punished foreign and transnational companies that worked with Iran, making them choose between doing business in Iran or in the U.S. Advocates and critics of the deal agree that these harsh sanctions forced Iran to the negotiating table. But critics of the deal who want to see Trump take action believe that the U.S. drew back that pressure too quickly — and that by reimposing sanctions, Trump will gain greater inspector access to Iran’s military sites, restrictions on its ballistic missile work and extensions on limits to its uranium enrichment.

The least aggressive scenario would be for Trump to impose only sanctions that directly affect Iran. (Not reinstating the sanctions against foreign businesses would avoid roiling the Europeans, who are fearful of the economic impact such a move would have on their companies doing business in Iran.) This path would likely “constitute significant non-performance” under the letter of the deal and could prompt an emergency session of the deal’s conflict arbitration mechanism. The parties would have 15 days to debate the matter, and a finding that the U.S. was in violation of the agreement would amount to a show of international solidarity against the Trump administration.

Among the possible withdrawal scenarios, this one would likely be the most welcome by Mattis and a bipartisan group of senators who are seeking a way to strengthen the accord by eliciting more constraints on Iran’s activities without gravely damaging the U.S.’s European alliances or taking steps with a higher risk of sparking armed conflict.

Although Iran could respond by resuming its nuclear work “in whole or in part,” according to the language of the deal, this is the most likely scenario in which Tehran remains within the agreement. Iranian officials have indicated that they will stay in the deal so long as it serves their “interests” — attracting foreign investment and protecting what currently exists, as well as combating U.S. influence in the region.

2. Trump reimposes all U.S. sanctions

A broad move reimposing all sanctions would mean that Trump has in practice withdrawn from the nuclear deal while putting the Europeans in a bind. EU banks and businesses would suddenly be subject to U.S. sanctions, an outcome that Europe appears to be preparing for by exploring emergency credit lines for EU businesses already invested in Iran.

Critics of the deal — including the Israeli government and some think tanks in Washington — believe this stronger action by Trump is necessary to force both Europe and Iran to agree to make the terms of the agreement stricter. But it could could trigger a trade war with Europe and increase the likelihood that Iran withdraws from the accord.

Still, even in this scenario, Iran might be tempted to remain within the deal alongside Russia, China and European powers if the result is an isolated United States — and if the government receives sufficient assurances that foreign investments will be protected.

3. Trump declares outright that the U.S. is abandoning the deal

Trump could formally announce that the U.S. is leaving the nuclear deal in an address modeled on his speech withdrawing from the Paris climate accord. While reimposing all the sanctions has the same de facto effect as such a declaration, an address would be an unequivocal and irreversible statement of U.S. policy, with little room for interpretation to give Iran more ability to save face.

A bipartisan consensus in Washington — which has brought together longtime critics as well as proponents of the deal — fears this outcome because of concerns that it would undermine U.S. credibility in future negotiations. Allies could see Trump’s pattern of withdrawing from international agreements as meaning that a U.S. commitment is only valid for the duration of a president’s term.

This path would likely increase the chances of a reciprocal Iranian withdrawal. But even still, there appears to be indecision within Iranian leadership over the best path forward should there be a brazen U.S. pullout if the right incentives with other global players stay in place.

4. Trump declares U.S. withdrawal and threatens military action against Iran’s nuclear facilities

Based on Bolton’s past rhetoric, this appears to be the path that he would advocate for — a militant approach that pulls the rug out from under the nuclear agreement. Bolton’s opposition to any deal with Iran seems to be based on a belief that it rewards and legitimizes a corrupt and dangerous government that can be fixed only through regime change.

U.S. military action would not be viable if U.N. nuclear weapons inspectors remained present in Iran’s military sites — monitoring now required under the deal — because of the risk of collateral damage. But if Iran itself were to withdraw from the agreement, it would likely kick out the international monitors to resume its enrichment and reprocessing of uranium, creating an opening for a U.S. attack.

An Iranian official said this month that Tehran would be able to quickly install state-of-the-art technology that the nuclear deal had temporarily suspended, allowing them to produce large amounts of highly enriched fissile material within a matter of weeks.

Still, what path Iran would take if the U.S. were to sharply escalate the situation in a short period of time is unclear. It is possible the Iranians would seek to remain in the deal, as in other scenarios, with European cover, but also possible that they would feel compelled to confront the U.S. with bold action of their own.