The chief of Iran's Atomic Energy Organization, Ali Akbar Salehi. (Leonhard Foeger/Reuters)

President Trump must decide by Thursday whether to once again waive economic sanctions on Iran, a task imposed on him by a deal he holds in contempt and appears to be preparing to ditch.

But despite his concern that Iran is an international threat, Trump is expected to waive sanctions on Iran's oil and banking sectors for the second time since taking office. If not, the United States will be in breach of the landmark 2015 deal that is a legacy of the Obama administration.

Even if Trump waives sanctions, as he must by law reassess every 120 days, it comes as Iran and the agreement it negotiated with six world powers are coming under increasing attack. In a series of public critiques of the deal and Iran's behavior, administration officials appear to be laying the groundwork to kill the existing agreement, possibly by finding a way to reopen it for modifications.

The next and most consequential decision on the horizon is Oct. 15, when Trump must decide whether Iran is fully complying with its commitments under the deal, known officially as the Joint Comprehensive Plan of Action. The president is required to revisit the issue every 90 days, and in July he reportedly was angry that his advisers offered no options except to certify it.

Many supporters of the deal believe it may not survive the year.

More than 80 nuclear nonproliferation specialists issued a joint statement Wednesday saying the agreement "has proven to be an effective and verifiable arrangement that is a net plus for international nuclear nonproliferation efforts."

Wendy Sherman, the chief U.S. negotiator in the talks, said leaving the agreement would drive a wedge between the United States and European allies who were its partners in negotiations.

"Either directly or indirectly, ripping up this deal by the United States is the worst thing we could do for American national security," she said, adding, "North Korea is watching closely."

The head of Iran's nuclear agency, Ali Akbar Salehi, said last week that if the United States walks away, Iran will adhere to the agreement with the other countries in the negotiations.

Trump's disdain for Iran's behavior and the nuclear deal predates his presidency. He campaigned vowing to "dismantle the disastrous nuclear deal with Iran."

If he waives sanctions again on Thursday, he may issue a strong statement condemning Iran or approving more sanctions on non-nuclear matters like terrorism support, ballistic missile testing or human rights.

Iran is expected to come under heavy criticism at the U.N. General Assembly next week, in speeches by both Trump and Israeli Prime Minister Benjamin Netanyahu.

At least some Europeans have indicated an openness to look for creative ways to strengthen the agreement, perhaps by negotiating a supplement, according to people familiar with the overtures. Administration officials are expected to raise the issue with their European counterparts in New York next week.

But other nations already are balking.

"We adamantly refuse to reopen the agreement," Gérard Araud, France's ambassador to Washington, wrote on Twitter on Tuesday.

"No renegotiation and respect of the agreement," he wrote in another tweet. "On this basis, we always can discuss other issues."

It is difficult for the administration to argue that Iran is violating the agreement, even if it backs militias in Syria and Yemen, has conducted a series of ballistic missile tests and is known for abusing human rights, including the imprisonment of U.S. citizens on flimsy charges.

But the International Atomic Energy Agency, which monitors Iran's nuclear facilities, has said eight times that Iran is in full compliance with its obligations.

Instead, U.S. officials have said Iran is violating the "spirit" of the agreement. In a speech before the United Nations, U.S. Ambassador Nikki Haley made the case that because of Iran's behavior, it may not be in the United States' national interest to stay in the deal.