While the public debate rages over President Donald Trump's threat to pull the United States out of the Iran deal, actors both inside and outside the U.S. government are planning for what happens the day after the United States exits — a scenario that looks increasingly likely.

Officials and lawmakers are nearly unanimous in their prediction that, if the United States and European partners are unable to agree on changes to the Iran nuclear deal, Trump will make good on his promise to scuttle U.S. participation in the deal. The president's next opportunity will come on May 12. If he declines to waive sanctions, the United States will be in breach of the agreement. Trump would likely announce America's exit then, prompting a series of responses and counter-responses around the world.

State Department policy planning director Brian Hook traveled to Europe last week and met with British, French and German officials to find a "fix" that meets Trump's standards. Expectations for success are low. If Trump does cancel the deal, experts say, the United States needs to be prepared in order to minimize the negative effects and optimize the U.S. negotiating position for the months and years ahead.

The State Department and the National Security Council have begun developing a diplomatic, economic and strategic communications strategy for pulling out of the deal, reimposing sanctions and dealing with potential responses from Europe, China, Russia and Iran. The work is not meant to influence Trump's decision, officials said, but to give the president the options he requested with responsible planning to back up each course of action.

The Trump administration laid out its terms for a supplemental agreement on Jan. 12. The list includes new restrictions on Iran's ballistic missile program, more intrusive inspections of its nuclear program and elimination of sunsets on restrictions on Iranian activities. Officials are making progress on the first two; Europeans are less amenable to extending the length of the deal.

The working assumption is that if the negotiations with Europe succeed, Iran will reluctantly accept the new constraints. "Iran has enormous economic incentives to stay in the deal and our assessment is they will stay in the deal if the E3 and the United States come to agreement on a supplement," the official said.

But if there's no agreement between the United States and Europe — and if Trump does not waive sanctions under the deal — things get very complicated, very quickly. The Treasury Department is working on the logistics of "snapping back" various sanctions, including restoring Obama-era executive orders that the deal rescinded.

After that, there's no certainty how other powers will react. The Foundation for the Defense of Democracies, a think tank that enjoys unique influence with the Trump administration, recently convened a group of about 20 senior Iran and non-proliferation experts to game out scenarios, the results of which were compiled in a memo. Half the experts favored a "fix" for the deal; half the experts favored a "nix."

The memo the FDD prepared, which has been shared with State, NSC and Treasury, argues that, regardless of the outcome, the Trump administration must begin preparing now in case the president pulls out of the deal.

Assuming Trump does declare America's exit, the FDD memo identifies "most likely" and "worst case" scenarios on a range of issues. It argues that Iran is most likely to stay in the deal, encourage other countries not to comply with U.S. sanctions, gradually increase its nuclear and missile activity, escalate activity of its regional proxy forces and pressure American to return to the deal. The worst-case scenario is Iran drastically ramps up its uranium enrichment and regional aggression, raising tensions and increasing the risk of a crisis.

Of course, Trump could avoid all of this by simply waiving the sanctions, as he has already done thrice, giving negotiators more time. But Trump is signaling that won't happen. So whether you like the Iran deal or not — whether you want to fix it or nix it — it's time to confront the reality that the United States might soon back out. In that case, all concerned would be well-advised to focus on preventing the worst-case outcomes. 

Josh Rogin is a columnist who writes about foreign policy and national security.