What's next for the Iran nuclear deal?

— -- The future of the Iran nuclear agreement is very uncertain after fresh condemnations by the Trump administration -- but looming on the horizon is the president's first big decision on whether the U.S. continues to abide by the deal.

In a sharply worded critique Wednesday, Secretary of State Rex Tillerson offered the administration's first serious statements on the fate of the Obama-era accord with Iran. And today, President Trump weighed in as well, blasting Iran for doing a "tremendous disservice" by not complying with the "spirit" of the agreement, which he again described as "terrible."

Specifically, Tillerson said that although Iran is in compliance, the Joint Comprehensive Plan of Action, or JCPOA, as the deal is officially known, only delays Iran’s goal of becoming a nuclear state - and that the Trump administration has no intention of passing the buck to a future administration. He railed against Iran for its support of terror, its missile development, and its meddling in deadly conflicts in Yemen, Syria, and beyond, and announced that in the next 90 days, the new administration would be developing its official Iran policy.

Trump echoed that promise Thursday, saying, "We're analyzing it very, very carefully, and we'll have something to say about it in the not too distant future."

So what happens next?

Before that 90-day policy review is finished review, the Trump administration will be faced with a decision that directly affects U.S. compliance with the deal.

A U.S. official said that on or around May 19 -- the same day as the Iranian presidential election -- the Trump administration will have to decide whether or not to extend some sanctions relief on Iran.

Under the deal, the U.S. agreed to eventually lift all nuclear sanctions against Iran -- what’s called transition day -- which is several years in the future. But in the interim, the U.S. has to continuously suspend those sanctions, using waivers which periodically come up for review. Before leaving office, Obama's Secretary of State John Kerry signed off on a number of waivers -- some which last 180 days, some 120, but the first of which will expired on May 19.

Before that day, the Trump administration has to decide, sign off on the waivers or let the sanctions go back into place.

If the State Department does not sign those waivers, it would be seen as a step towards dismantling the nuclear agreement.

This issue is entirely separate from the letter that Tillerson sent House Speaker Paul Ryan Tuesday night, certifying that Iran was complying with the deal. That was a purely domestic obligation - not actually part of the JCPOA itself, but the Iran Nuclear Agreement Review Act of 2015.

Another significant date is April 25, when signatories to the Iran deal meet in Vienna, essentially for an 'airing of grievances,' where they'll be hashing out any complaints. The Secretary of State is not expected to attend. It will be lower level officials only.