President Trump signaled this week that he wants to renegotiate the Iran deal, which he has criticized as “one-sided” and an “embarrassment” to the United States, but exactly how he will do it is not yet clear.

He and his top advisers are hinting that he might not certify that Iran is complying with the Iran deal by a deadline of October 15, which would give Congress 60 days to decide whether to re-enact sanctions.

On Wednesday, Trump told reporters he has decided on whether to recertify Iran’s compliance, but didn’t say what he would do. “I have decided,” he said. “I’ll let you know.”

The week before, he told reporters, “You’ll see what I’m going to be doing very shortly in October.” He called the “spirit” of the deal “atrociously kept.”

The Trump administration has argued that although Iran is in “technical compliance” with the deal, it is violating the aspirations of the deal by continuing to develop ballistic missiles, support terrorist groups, and smuggle weapons.

On Wednesday, the commander of U.S. Strategic Command Air Force Gen. John Hyten said Iran was operating under the agreement, but at the same time, “rapidly” deploying and developing ballistic missiles.

“Iran is operating under the agreements that we signed up for under [the Joint Comprehensive Plan of Action],” he said at the Hudson Institute. “But at the same time, they’re rapidly, rapidly deploying and developing a whole series of ballistic missiles and testing ballistic missiles of all ranges that provide significant concerns not just to the United States but our allies.”

“And why are they doing that? They’re doing that to challenge the United States and our allies somewhere down the road and so we have to figure out how to respond to that,” he said.

Reimposing sanctions could either blow up the deal or leave the U.S. outside of it. But the threat of sanctions could pressure Iran and international partners back to the negotiating table. Trump could also decide to certify in October in exchange for new negotiations.

Alternately, Trump could call for a separate agreement that would deal with Iran’s behavior outside of the nuclear deal.

U.S. ambassador to the United Nations Nikki Haley on Thursday suggested that if Trump did not recertify, it would not automatically mean the end of the U.S.’s adherence to the deal.

“If he still thinks that the deal is in the best interest of the United States, then he certifies. If he thinks that the deal is—that the situation is not in the best interest of the American public, then he doesn’t certify. At that point, it goes to Congress and he works with Congress on how to reshape the situation,” she said.

Trump and top U.S. officials this week at the United Nations General Assembly discussed the issue with members who took part in negotiating the Iran deal.

According to White House statements, Trump on Wednesday discussed “next steps” with British Prime Minister Theresa May and “exchanged views” with French President Emmanuel Macron.

Macron signaled openness to a follow-up agreement, saying that the deal was no longer enough to safeguard against growing power of Tehran in the Middle East.

According to reports, Trump wants to extend the deal’s time frame, since some of its provisions expire in as few as 10 years. He also wants to impose new limits on Iran’s development of ballistic missiles.

Iran so far has signaled it would not revisit the agreement, with Iranian President Hassan Rouhani calling it a “closed issue,” threatening to start enrichment of uranium.

European Union Foreign Minister Federica Mogherini on Wednesday evening rejected scrapping or renegotiating the agreement, which she said was working.

House Foreign Affairs Committee Chairman Ed Royce (R-CA) has suggested strictly enforcing the agreement instead of scrapping it.

On Thursday, 45 national security experts signed a letter urging Trump to withdraw from the deal altogether and impose strict new sanctions on Iran.