The Trump administration is preparing to enforce international sanctions against Iran that most other countries intend to ignore, testing the ability of the United States to impose its will on the rest of the world.

The decision to plow ahead with a step that many other governments fear could kill the 2015 nuclear deal with Iran is the culmination of more than three years of growing tensions between Washington and Tehran. Secretary of State Mike Pompeo has branded Iran an “evil force” in the region. President Trump has called the landmark nuclear agreement the “worst deal ever negotiated” and withdrew from it in 2018.

Now, only weeks away from the election, the Trump administration is making its boldest move yet against Iran by triggering the “snapback” of U.N. sanctions that were lifted as part of the deal, a legal interpretation shared by only a handful of U.S. allies. Trump is expected to sharply criticize Iran and claim victory in beating back its more egregious behavior when he speaks to the United Nations General Assembly next week, an annual diplomatic extravaganza pared down to virtual appearances by most world leaders because of the coronavirus pandemic.

The United States claims that, as an original participant in the deal, it has the legal right to force reimposed sanctions over the objections of the other countries that negotiated the agreement. The U.S. case was rebuffed in a Security Council meeting last month, as every member except the Dominican Republic argued the United States gave up the authority to do so when it left the deal.

Even as U.S. officials are making concrete plans to slap sanctions on countries and banks that facilitate trading with Iran when an arms embargo expires, most countries at the United Nations are treating it as a nonevent.

“No one’s recognizing it,” said a Western diplomat, speaking on the condition of anonymity about the open defiance planned.

“The U.S. can take unilateral sanctions and say they’re part of snapback. But there’s not much more they can do. The council itself will actively ignore it. And hope elections go a certain way.”

Pompeo and Elliott Abrams, the special envoy for Iran and Venezuela, have declared that the United States will immediately begin enforcement this weekend.

In Suriname on Thursday, Pompeo said Washington expects every country to uphold the sanctions, despite any misgivings.

“The United States is intent on enforcing all the U.N. Security Council resolutions, and come Monday, there will be a new series of U.N. Security Council resolutions to be in force, and we intend to ask every country to stand behind them,” he said.

Abrams said the sanctions will bounce back into place at 8 p.m. Saturday. That could give pause to arms dealers who may have been preparing to sell conventional weapons to Iran after an embargo expires in mid-October under a clause in the nuclear deal, Abrams said. The October date will be “less significant,” he added, once all sanctions are resumed.

U.S. officials say their decision was prompted by the looming embargo expiration, which would allow countries to engage in the trade of conventional weapons with Iran and abet Tehran’s support for Shiite militias in neighboring countries. During negotiations for the nuclear deal, Iran insisted on the embargo ending as a condition for limiting its nuclear program. The Western countries agreed to it reluctantly, reasoning Iran’s nuclear program was a greater threat.

Although China and Russia are both keen to engage in arms trade with Iran, they are unlikely to do anything before the arms embargo outlined in the nuclear deal expires next month.

“The October deadline matters,” said Behnam Ben Taleblu, an Iran analyst with the Foundation for Defense of Democracies. “On the first sale or transfer of weapons, Washington will immediately have to come down on the entity or bank that facilitated this transfer. So Washington will be in an interesting place as it uses unilateral sanctions to enforce multilateral purposes. It will have to, until more countries believe the United States is entitled to engage in snapback or Iran’s behavior merits it.”

The European Union, which shares U.S. concerns about Iran’s ballistic missile testing and support for militants in the region, fears the resumption of all sanctions could doom the nuclear agreement with Iran entirely. Josep Borrell, the E.U.’s foreign policy chief, said last month that the United States is not a participant and has no right to impose snapback sanctions under the deal it left.

“I will continue to do everything possible to ensure the preservation and full implementation of the JCPOA by all,” he said, using the acronym for the nuclear deal’s official name, the Joint Comprehensive Plan of Action. “The JCPOA remains a key pillar of the global nonproliferation architecture, contributing to regional security.”

Abrams said details on how the United States plans to enforce the sanctions will be rolled out in coming days.

“We will have some announcements over the weekend and more announcements on Monday, and then subsequent days next week as to exactly how we are planning to enforce these returned U.N. sanctions,” he said.

“And whether those countries will in fact ignore the U.N. sanctions remains to be seen,” he added.

In the short term, the ramifications are likely to be minimal.

“Due to the breadth of U.S. sanctions on Iran, and some of the remaining E.U. restrictions on Iran, it’s not clear how much trade is going to be affected,” said Kelsey Davenport, director of nonproliferation policy at the Arms Control Association. “I think this is a very symbolic move by the United States that’s part of a concerted effort to kill the JCPOA.”

Although Tehran has threatened several retaliatory steps, including walking away from the nuclear agreement and ramping up its nuclear program again, President Hassan Rouhani on Wednesday described Iran’s overwhelming opposition to Washington’s move as a “victory of the Iranian nation and the disgraceful defeat of the United States in activation of the snapback mechanism.”