President Trump’s decision to withdraw from the Paris Climate Accord was the latest in a steadily expanding list of actions that highlight his contempt for multilateral diplomacy in U.S. foreign policy. This does not mean that Trump is an isolationist. He clearly favors bilateral engagement with other countries and doesn’t mind using American military power to wage war in the Middle East and apply pressure to North Korea. The question is, what does Trump’s withdrawal from the Paris agreement mean for other areas of multilateral engagement?

A preference for bilateral over multilateral diplomacy may be appropriate in some cases, but the bilateral approach is not ideal for combating, for example, nuclear proliferation. Trump’s disdain for multilateral diplomacy is especially worrisome when combined with the deepening militarization of U.S. foreign policy. These two emerging trends simultaneously endanger the Iran nuclear deal, a major success for multilateral diplomacy and nuclear nonproliferation, while increasing the probability of armed conflict should the deal fail.

The Iran deal is a triumph of multilateral diplomacy, involving the United Nations’ Permanent Five (United States, United Kingdom, France, Russia, and China), Germany, and the European Union. This level of international involvement enhances both the legitimacy and strength of the agreement, which Iran has complied with since implementation began in January 2016. If the Trump administration wants to successfully renegotiate the deal, it would need the buy-in of the partner countries, a condition that becomes harder to achieve as Trump alienates many of our Iran deal partners with actions such as withdrawing from the Paris Climate Accord.

If Trump truly wants to renegotiate the Iran deal (and not just unilaterally withdraw from it), then he will need the support of the very countries that he is repeatedly frustrating with his characteristically undiplomatic actions on the world stage.

The other major nuclear challenge facing the Trump administration is North Korea. So far, the administration has tried to rein in the North’s nuclear weapons and ballistic missile programs through shows of military force and sanctions. Trump also wants China to do more to pressure North Korea. Pyongyang does not seem deterred by this approach. While there has not been a nuclear weapons test since Trump took office, there has been a steady march of successful ballistic missile tests and Kim Jong Un continues to place great value in his nuclear arsenal.

A multilateral diplomatic approach failed to bring North Korea to heel in the 2000s, so it makes sense that Trump would not place much confidence in a similar approach today. The administration has made no serious overt attempt at multilateral diplomacy besides introducing new sanctions via the United Nations. If the current approach of pressure fails to halt North Korea’s progress, the administration could choose to double down on their approach or try a different strategy that makes greater use of multilateral diplomacy. Trump’s aversion to multilateral diplomacy suggests that the administration is primed to keep ratcheting up pressure rather than change course.

While this latest withdrawal from a multilateral initiative is not the end of the world, it arguably has worrisome implications for nuclear nonproliferation. Multilateral cooperation is not necessary to solve every foreign policy problem, but it is incredibly valuable for preventing the spread of nuclear weapons. The sooner Trump and his advisors realize this, the better.