During the Republican primary season, most candidates railed against the Iranian nuclear deal promising to rip it up. Indeed, Donald Trump, our new President-elect, described the Joint Comprehensive Plan of Action (the JCPoA) as “one of the worst deals I’ve ever seen.” With Trump’s unexpected success in yesterday’s election, the future of the Iran deal—one of the major diplomatic successes of Barack Obama’s presidency—has become murky.

Over the last year, Trump’s campaign was impressively inconsistent on the question of the Iran deal. Various Trump surrogates—including Rudy Giuliani in his speech at the Republican National Convention—suggested that Trump would “rip up” the deal on day one in office. Trump himself strongly criticized the deal, promising in a speech to AIPAC in March that dismantling the deal would be his number one priority. Yet later statements focused instead on the idea that he would “fix” the deal, by going back to the negotiating table with Tehran, a line later adopted by many of his campaign advisors.

Unfortunately, though this might indicate that Trump’s stance was more rhetoric than reality, he is likely to face strong pressure from the GOP-dominated congress to upend the deal. The pressure is liable to come from inside his administration too: not only did Mike Pence, Trump’s VP pick, take a hard line on the Iran deal in debates, but several of Trump’s potential advisors have similarly argued that the deal should be destroyed. It’s hard to imagine an administration featuring Bob Corker, John Bolton or Michael Flynn taking a conciliatory approach to Iran on any issue.

So can Trump actually end the Iran deal? Perhaps more effectively than many have assumed, though it would be politically and diplomatically costly. In order to end the deal, the United States would have to assert to the UN Security Council that Iran is violating the agreement. Though such a violation would technically be confirmed by an external party like the IAEA, the fact is that the “snapback” provision of sanctions relief found in the JCPoA allows the United States to exercise its veto power, forcing the reintroduction of UN sanctions.

The United States cannot force the European Union to reintroduce all its sanctions, which include some of the harshest measures on Iran’s oil and banking sectors. Nor can it apply sanctions retroactively; companies cannot be punished for deals made since sanctions were lifted (like the Total oil and gas deal). But if he wanted to, President Trump could issue executive orders reinstating or creating new sanctions on Iranian individuals or companies. He could also direct the Treasury to apply those sanctions extraterritorially, preventing European or Asian companies which do business with Tehran from accessing the U.S. financial system.

Yet the choice to end the Iranian nuclear deal would be extremely costly for the United States. It would alienate key allies in Europe and elsewhere, discouraging them from participation in future U.S. diplomatic endeavors. A better deal is pretty much impossible to achieve, thus we would substantially increase the likelihood that Iran will return to nuclear development, bringing them closer to the bomb, and the United States closer to military conflict. And it would be a black eye for the United States, implying that we cannot be trusted to abide by international agreements which we negotiate.

It’s certainly possible for President-elect Trump to dismantle the JCPoA. But as with all questions about Trump’s foreign policy, it remains unclear whether he will choose to do so or not. If he does, the repercussions for U.S. foreign policy would be unpleasant. Tearing up the Iran deal may look good to the Republican base, but it’s the diplomatic equivalent of shooting ourselves in the foot: it achieves no foreign policy goals, runs the risk of destabilizing the Middle East still further, and does grave harm to America’s diplomatic reputation.