LONDON — If confirmed as secretary of state, Mike Pompeo will arrive at a department that has been battered by proposed budget cuts, hollowed out by resignations and vacancies, and neutered by President Trump’s impulsive and personal decision-making style. But Pompeo’s most immediate challenge will not be rebuilding the department and restoring morale; it will be dealing with an acute foreign policy crisis that is largely of the president’s own making — the Iran nuclear deal.

Pompeo will have to tackle a genuine foreign policy challenge soon. President Trump has agreed to meet with Kim Jong Un before the end of May. This could be a promising development, defusing the rising tensions on the Korean peninsula and across Asia. Yet before Trump even sits down with Kim at the negotiating table to discuss a nuclear deal, the administration will have to decide how to handle the preexisting deal with Tehran.

Trump has already announced that America will no longer abide by the Iran nuclear pact unless European leaders agree to “fix the deal’s disastrous flaws.” (And from the outset, he has been cheered in his hard-line posturing by Pompeo.) European nations seem unwilling to endorse more than cosmetic changes, and Iran has flatly refused to renegotiate. That means by May 12 the United States is set to pull out of the agreement, which could lead Iran to do the same and restart its nuclear program. This would happen at the very same time as the summit with North Korea — when the U.S. will surely be trying to convince North Korea of the benefits of signing a similar agreement.

To understand the virtues of the Iran deal, recall that a quarter-century ago, the United States was negotiating a nuclear accord with Pyongyang. At that point, North Korea had a nuclear program but no nuclear weapons. The Clinton administration was trying to get the regime to freeze its program, agree to some rollbacks and allow intrusive inspections. But the accord that was ultimately reached was far more limited than hoped for. The inspections process was weak, and the North Koreans cheated.

The Iranians in 2015 also did not have nuclear weapons (and insisted they had no intention of ever making them). Still, the nuclear deal required them to scale back significant aspects of their program, dismantling 13,000 centrifuges, giving up 98 percent of their enriched uranium and effectively shutting down their plutonium reactor at Arak. The International Atomic Energy Agency has cameras and inspectors in Iran at every stage of the nuclear fuel cycle — from mines to labs to enrichment facilities. The IAEA attests that Tehran has abided by its end of the deal. Even Pompeo himself has conceded as much.

The Iran accord is not perfect, but it has stabilized a dangerous and spiraling situation in the Middle East. Were the deal to unravel, an already simmering region would get much hotter. (The crown prince of Saudi Arabia, Mohammed bin Salman, recently affirmed that his kingdom would go nuclear if Iran did.) And, again, this would all be happening just as the Trump administration would be trying to convince the North Koreans to agree to limits, freezes, rollbacks and inspections of its own nuclear program. Why would Kim sign a deal while he watches the United States renege on the last one it signed?

The tragedy here is that this is an entirely self-inflicted crisis. There was already enough instability in the world that the administration did not need to create more. Pompeo should recognize that his job as secretary of state will be to solve problems, not produce them, and he should preserve the Iran accord and spend his time on North Korea. But that would still leave a considerable challenge regarding North Korea’s nuclear weapons. There, too, the administration’s position — and his — has been maximalist, vowing to accept nothing less than the total denuclearization of North Korea. But that’s a negotiating position that can and should be adjusted over time, depending on North Korean behavior.

Pompeo should take a page from his boss’s book. Trump has reversed course on issue after issue, often with little explanation. He declared that NATO was obsolete only to say later that it was not. He promised to label China a currency manipulator and then decided against it. He insisted that talking to North Korea would be a waste of time and then eagerly announced that he would. And who knows, maybe Trump understands the public’s inattention and mood better than most of us. In any case, whatever Pompeo said about the Iran deal months ago is now ancient history. He should simply declare that right now, under the circumstances, the deal is worth preserving.

There are significant costs to the nation’s credibility and reputation if Washington keeps reversing its positions on core foreign policy issues. Yet there are greater costs to stubbornly persisting with the wrong policy. So Mr. Pompeo, repeat after me: “The Iran deal was bad, but now it’s good.”

Fareed Zakaria is a columnist with The Washington Post. His email address is: comments@fareedzakaria.com.

Fareed Zakaria