The United States is alarmingly close to getting dragged into yet another military entanglement in the Middle East, this time by Israel — which is looking less and less like a true friend.

Israel’s surprise attack on Iran on Friday has almost certainly blown up any chance of reaching the nuclear deal the United States was pursuing for months. Prime Minister Benjamin Netanyahu of Israel has also recklessly endangered the 40,000 U.S. troops deployed in the region, putting them at immediate risk of Iranian retaliation, which could draw America into a war with Iran.

However Iran interprets our role in the attacks, Israel appears to have acted without giving the United States enough warning to take adequate precautions. Though President Trump acknowledged on Thursday that an Israeli attack might be imminent, the United States only began voluntary evacuations of military families and nonessential embassy personnel on Wednesday afternoon, while the State Department began drawing up plans for mass evacuation of U.S. citizens mere hours before the attack.

Mr. Trump, and all Americans, should be furious. Now Mr. Netanyahu and hawkish voices in the United States will almost certainly put pressure on Mr. Trump to assist Israel in destroying Iran’s nuclear enrichment sites, something that will be difficult for the Israeli military to do on its own and that even the U.S. military might be unable to accomplish. It would be the worst mistake of Mr. Trump’s presidency.

The misguided 2003 invasion of Iraq was also a war to forestall nuclear proliferation. Disaster ensued, and not just because Saddam Hussein didn’t have weapons of mass destruction. The U.S. invasion triggered chaos and civil war in Iraq and tipped the regional balance of power toward Iran by allowing it to establish new proxy militias in the country. It also led to the eventual rise of ISIS.

There is no reason to think that a war with Iran would go any more smoothly — and it could turn out considerably worse. If drawn in, the U.S. military’s involvement would likely begin with airstrikes rather than a ground invasion, given Iran’s large size and forbidding mountainous terrain. But as the fruitless $7 billion campaign against the Houthis showed, airstrikes are exorbitantly expensive, entail significant risks of American casualties and are likely to fail anyway. The United States never even gained air superiority over the Houthis, a ragtag militant group with the resource base of an impoverished country, Yemen, over which it couldn’t even consolidate control.

Iran is far more capable of defending itself than the Houthis are. If airstrikes fail to destroy Iran’s nuclear capabilities, pressure would dramatically increase on U.S. forces to pair an aerial barrage with a ground component, perhaps something akin to the “Afghan model” the United States used to topple the Taliban. We know how that went. Despite the intent to keep that war small and brief, an engagement that started with just 1,300 U.S. troops in November 2001 snowballed into a disastrous 20-year occupation that reached some 100,000 U.S. troops at its height in 2011 and ultimately caused the deaths of 2,324 U.S. military personnel.

Assuming some continuity of technical knowledge persists, Iran would likely be able to rebuild its nuclear facilities quickly. And a defiant Iranian regime would no doubt be determined on weaponizing to deter future Israeli and U.S. attacks.

That likelihood, coupled with Israel’s insistence that Iran must never get the bomb, suggests that Mr. Netanyahu’s theory of victory could be premised on an underlying logic of regime change. Supporting that point, Israel appears to be engaging in strikes aimed at disabling the regime’s leadership in Tehran.

The Israeli leader has long embraced the desirability of regime change in Iran, and hinted in September that it could happen “sooner than people think.” As a French diplomatic source told Le Monde last fall, “The idea is circulating in certain circles that perhaps the Israelis are leading us toward a historic moment, that this is the beginning of the end for the Iranian regime.” The fall of Syria’s Bashar al-Assad in December intensified speculation about similar upheaval in Iran. Some U.S. policy hawks and members of the Iranian diaspora now claim regime change is becoming inevitable; as Mr. Trump’s former national security adviser John Bolton put it, “It’s now time to think of the campaign for regime change in Iran.”

That is magical thinking. History has shown again and again that bombing a country turns its people against the attacker, not against their own regime, despite its deep unpopularity. Images already show Iranians demonstrating in the streets — not to oppose their government but to urge retaliation against Israel. And even if the regime were to be deposed, what then? For all the Iranian government’s faults, a bad government is preferable to the chaos of no government. Do we really want to turn Iran into a failed state, like Iraq or Libya after the United States attacked those countries?