How do you deal with an Islamic state that oppresses its own citizens, sponsors terrorist organizations, sends guerrillas to stir up trouble in neighboring countries, calls for the genocide of Jews, stockpiles long-range missiles, then works hard to build nuclear warheads to place on top of those missiles? There can be no illusions about making peace with this kind of rogue regime. The only question is how to contain them in such a way as to prevent all-out regional war.

Reasonable people disagree about how to get there. Barack Obama believed that the best path was through diplomacy that was tightly focused on limiting the most dangerous aspect of the Iranian regime—nuclear proliferation—and striking a deal that would keep the ayatollahs from reaching their goal. Donald Trump thinks otherwise. He believes that containing Iran’s bad behavior requires a more comprehensive approach. On Tuesday, he announced that the United States will be withdrawing from the Iran deal.

I understand both arguments but lean more strongly toward Trump’s. The Iranian regime is the single biggest force for instability in the Middle East. Iranian provocations in the region have only increased, not decreased, since the nuclear deal was signed. Iran is still perpetuating the civil war in Syria, still running proxy forces in Lebanon, Iraq, and Yemen, still chanting death to America, still calling for the destruction of Israel, and still working with rogue actors around the world to undermine our interests.

Trump’s approach understands that strength is the best posture with which to engage a rogue state. It also recognizes the inherent weakness of the Iranian regime: a plummeting economy, an unhappy population, and a military that is overstretched and exhausted. Many commentators portray Iran as a juggernaut that must not be angered; but although Iran is dangerous, it is far less powerful than most people think.

There are other reasons to like the Trump decision, the most obvious one being the expressed wishes of our local allies. That sound you heard yesterday was wild cheering from Jerusalem, Riyadh, and the Gulf. Trump’s withdrawal from the Iran deal also checks the momentum of Russian and Iranian expansion in the Middle East, letting both regimes know that the US will not stand by while they gobble up the region. The decision also sends a message to external actors, like North Korea, that America is playing a serious game.

But there are reasons to be concerned, too. Iran is weak, but weak regimes that feel cornered can sometimes be the most dangerous. The odds of sudden escalation at the Syria-Israel-Lebanon border are now much greater. Israel has already launched at least one preemptive strike into Syria to signal its own refusal to back down, and yesterday warned its citizens that war may be coming this summer. The odds of Israel or the US bumping into Russia and sparking a much larger conflagration have increased as well.

Also, there is Iran’s nuclear weapons program. What happens now? Will the ayatollahs abandon the deal altogether, or stay committed to the European states that still remain parties? Will the Iranian regime take symbolic steps toward restarting their nuclear program, or will they redouble their efforts in a mad dash to achieve nuclear breakout? The answers are unclear, but it seems unlikely that Tehran will take Trump’s challenge lying down.

And what about sanctions? Trump announced, “We will be instituting the highest level of economic sanction. Any nation that helps Iran in its quest for nuclear weapons could also be strongly sanctioned by the United States.” Will these sanctions be crafted in such a way as to contain and undermine the regime while minimizing the harmful effects on the Iranian population? Sometimes sanctions, if levied poorly, can have the effect of increasing support for an unpopular regime.

All of these concerns are exacerbated by Trump’s desire to get out of the Middle East as fast as possible. Defeat ISIS and go home—that’s been his policy since day one. But disengaging from the region is utterly at odds with his policy of containing Iran. The expansion of Iranian power has been commensurate with American withdrawal, and the rollback of Iranian power will likewise be in proportion to American reengagement in the region.

If Trump wants a comprehensive response to Iran, he better be prepared to stay engaged for the foreseeable future. Abandoning the nuclear deal only makes sense if the US is prepared to remain in the Middle East. His announced retreat from eastern Syria—the only ground we really hold at this point—would be a catastrophe in a post-deal world.

Trump could have chosen the deal. He could have chosen retrenchment. But he could not choose both.

The moral dimensions of the situation are clear: the Iranian regime is oppressive, warmongering, and genocidal and needs to be stopped. But if the US is serious about containment, the US needs the strategic insight and political will to go for the long haul. Some of our worst mistakes in the Middle East have been due to half measures. Trump made a decision, and the most important thing now is to follow that decision through.

Robert Nicholson is the executive director of The Philos Project and co-publisher of Providence.

Photo Credit: A ballistic missile is launched and tested in an undisclosed location in Iran on March 9, 2016.