Donald Trump will be a busy man January 20 as he nominates new cabinet secretaries and seeks to reshape a post-Barack Obama agenda in domestic and international affairs.

Among the issues he will confront is whether to continue U.S. compliance with Obama’s chief foreign policy legacy: the landmark nuclear agreement reached with Iran last year.

During the campaign, Trump harshly criticized the Joint Comprehensive Plan of Action (JCPOA), calling it “horrible, disgusting, absolutely incompetent” and suggesting it should be renegotiated. At other times, he merely vowed to “police that contract so tough that they don’t have a chance” and to counteract any violations with “tough, new sanctions.”

There is reason to hope that Trump will not walk away from the agreement assuming Iran continues to comply with it. For one thing, it is a multinational accord blessed by the United Nations and negotiated with Iran by five countries in addition to the United States: Russia, China, France, Britain and Germany.

It is worth recalling, however, that the JCPOA barely survived Congressional scrutiny last year when a nearly united Democratic caucus prevented the Senate from holding a vote on the deal. It is thus equally vital that the incoming Congress does not sabotage the JCPOA by seeking to re-impose sanctions on foreign companies that do business with Iran. That would be a clear violation of the agreement and might provoke an adverse Iranian reaction.

As the lame-duck Congress returns next week, one option would be for legislators to pass a simple extension of the Iran Sanctions Act, which threatens to penalize foreign companies that invest in Iran’s oil and gas sector and is due to expire at the end of the year. Then President Obama could immediately waive the legislation, as required by the JCPOA.

That would satisfy the argument of JCPOA critics that the next president needs something to “snap back” if Iran violates the agreement. And it would give Trump a good excuse to avoid making any new decisions about Iran.

If the U.S. were to re-impose sanctions absent a compelling reason, it is unlikely that Russia, China and the Europeans would follow suit. Indeed, in the aftermath of the U.S. presidential elections, Iranian President Hassan Rouhani and Foreign Minister Javad Zarif expressed confidence that Trump would comply with the JCPOA because of its multilateral character.

However, there is another concern that may be more difficult to assuage. Many European companies – in particular banks – were waiting until the U.S. election before concluding business deals with Iran, anticipating a victory by Hillary Clinton, a defender of the JCPOA. Now the risks of doing such business will rise even more because of uncertainty about Trump and the next Congress.

There is also anxiety about the impact of the Trump victory on Iran’s domestic politics. Iranians had already been grumbling about the lack of tangible benefits from the JCPOA; if foreign companies shy away from trade and investment, Iranians may blame Rouhani – who himself faces re-election next May.

The United States has already declined mightily in Iranian public opinion because of the slow pace and limited distribution of economic gains from the JCPOA. Now the U.S. image has been further tarnished by the vulgar and divisive nature of our presidential campaign.

Hardliners in Iran are celebrating the Trump victory, figuring that he will not attempt to improve relations with Tehran and will certainly not promote democratic values abroad. They have also noted an element of apparent agreement between Trump, Russia, Iran and the Syrian government of Bashar al-Assad on the need to focus on the threat of the Islamic State group rather than on changing the Assad regime.

Other Iranians are more nervous about the possibility that U.S.-Iran relations will deteriorate and lead to violence. Some posted comments on the Facebook page of Trump’s daughter, Ivanka, urging her to persuade her father to stick with the agreement and not embrace a hostile policy toward Iran.

The Atlantic Council recently published a report advising the next administration to take risks and seek better relations with Iran. That now appears doubtful. But at least Trump and the new Congress should leave well enough alone and let the nuclear agreement stand.

Barbara Slavin is Acting Director of the Future of Iran Initiative at the Atlantic Council’s South Asia Center.