President Donald Trump announced Tuesday he would reimpose sanctions on Iran, dealing a likely fatal blow to the 2015 multinational nuclear deal and upsetting European countries, Democrats and even some Republicans.

But though Trump’s action is aimed at punishing Iran, it is anger from U.S. allies, especially France, Germany, and the United Kingdom, that could most affect the United States in the coming weeks and months.

Speaking at the White House, Trump said he would not sign a new waiver for congressionally imposed sanctions that were lifted by President Barack Obama in early 2016 as implementation of the nuclear accord went into effect.

Watch: Trump Announces Withdrawal From Iran Nuclear Deal

“We cannot prevent an Iranian nuclear bomb under the decaying and rotten structure of the current agreement,” Trump said, announcing that he would begin reinstating “U.S. nuclear sanctions on the Iranian regime” and at “the highest level of economic sanction.”

But leading Republican policy voices in Congress have distanced themselves from Trump’s position on Iran, including House Armed Services Chairman Mac Thornberry of Texas and House Foreign Affairs Chairman Ed Royce of California. Royce noted on Tuesday some of the deal’s concessions to Iran are irreversible, including returning roughly $50 billion in formerly frozen assets.

“Tearing up the nuclear deal will not recover this cash,” Royce said at a committee hearing on Iran. “That toothpaste isn’t going back into the tube. It also won’t help galvanize our allies into addressing Iran’s dangerous activities that threaten us all. I fear a withdrawal would actually set back these efforts. And Congress has heard nothing about [an] alternative.”   

Thornberry said he would have preferred to give European allies a few more months to strengthen the deal. Nonetheless, he stressed that a “strong, international effort” is required to curtail Iran’s aggressive behavior.

“Now that the President has decided that the United States will withdraw, we must have two critical priorities,” he said in a statement. “One is to further enhance our own military capabilities.  The other is to strengthen our alliances.”

Lawmakers are worried about opening a rift with Europe that isolates the United States as it seeks to rally international support for high-stakes nuclear diplomacy with North Korea and for pushing back on multiple fronts against China’s regional ambitions.

Senate Foreign Relations Ranking Member Robert Menendez, who authored major congressional sanctions on Iran while also opposing the 2015 deal, castigated Trump for his decision to withdraw without a clear path forward. The New Jersey Democrat demanded a congressional briefing on how Iran would be prevented from acquiring a nuclear weapon absent the multinational accord.

“The governments of Iran, Russia, and China will seize this opportunity of self-imposed U.S. isolation to continue major weapons sales, deepen economic ties, and further challenge the United States and Europe not only in the Middle East but in other areas like North Korea,” Menendez said.

Though Trump has already withdrawn from international agreements including the Paris Climate Accord and the Trans-Pacific Partnership, lawmakers are concerned that abandoning the Iran accord, which took years to negotiate, could haunt the United States in future multilateral negotiations.

“Our allies and adversaries alike will not trust American leadership to negotiate another agreement whether on Iran or North Korea or elsewhere,” said Rep. Gerald E. Connolly, D-Va., in prepared remarks for the Tuesday Iran hearing.

No real ‘Plan B’

The president and his supporters say they believe the might of the U.S. financial system can inflict a strong enough economic punishment to eventually coerce Tehran into seeking new nuclear negotiations — ideally after the Iranian people have successfully pushed for a bloodless regime change.

Under such circumstances, they argue that Tehran would agree to nuclear and missile concessions the Obama administration and other world powers were unable to achieve.

But members of both parties have said that without the support of the European Union — let alone China, Russia and other major economic powers like Japan and South Korea — the United States does not have the economic leverage to cripple the Iranian regime. Congress in the 1990s, for instance, passed harsh oil sanctions on Iran that were not enforced until the Obama administration prodded Europe to support them as a means of getting Tehran to the negotiating table.

This time around, support from Europe for Trump’s hard-line approach is essentially non-existent.

The European Union, including major negotiating partners France, the United Kingdom and Germany, says it will not join the United States in imposing sanctions on Iran as Tehran has not violated the terms of the nuclear agreement.

“We are determined to save this deal because this accord safeguards against nuclear proliferation and is the right way to stop Iran getting a nuclear weapon,” French Foreign Minister Jean-Yves Le Drian said to reporters in Berlin on Monday, according to press reports.

EU officials have warned if the United States re-imposes secondary sanctions for doing business with Iran then the European Union would respond by reviving “blocking” regulations it issued in the 1990s that directed European companies not to comply with congressional sanctions on Iran.

“This is not to say that Europe will follow that path but that is certainly a possibility,” said former deputy secretary of State Anthony J. Blinken, a supporter of the nuclear agreement, in a Tuesday conference call with reporters. “The bottom line of this decision this afternoon is that it will precipitate a conflict either with Iran or with our allies.”

Some Iranian government figures have warned their country would quickly resume the uranium enrichment work the deal currently bans. But some analysts speculate Tehran’s smart play would be to remain compliant with the accord, thus leaving the United States to absorb all the international opprobrium for violating the deal.

American withdrawal from the Iran deal jeopardizes several large airplane deals struck by European and American firms, including two agreements by Chicago-based Boeing Co. worth roughly $20 billion to sell a total of 110 aircraft to two Iranian airlines. Similarly, the European consortium behind Airbus may have to cancel a $19 billion planned sale of airplanes to Iran as it relies on many American-made aircraft parts, which are subject to Treasury Department restrictions.