America’s entry into the Iran-Israel conflict early Sunday morning appears, on the surface, to be a triumph for the hawkish wing of the GOP. Advocates for realism and restraint in American foreign policy, who appeared ascendant in the early days of Trump 2.0, now find themselves bracing for the possibility of a wider war in the Middle East.

President Trump has framed America’s surgical strikes on Iran’s three key nuclear enrichment facilities as a one-and-done deal to decapitate the nation’s nascent nuclear ambitions. On Sunday, the Pentagon confirmed all the sites sustained “extremely severe damage,” though it emphasized that a full assessment of the attack will take time. Vice President Vance proclaimed that “we’re not at war with Iran; we’re at war with Iran’s nuclear program.”

Those who previously held hope in President Trump’s “America First” platform are expressing fear that the door to further escalation in the region has now been flung open. In a sign of what could come, Mr. Trump made it clear on Saturday that if Iran does not seek a peace deal with Israel, “there will be tragedy for Iran far greater than we have witnessed over the last eight days” — to which the Iranian foreign minister, Abbas Araghchi, declared that Iran “reserves all options” for its response.

The ramifications are already becoming clear. American troops and bases in the region are now vulnerable. Iran has threatened to shut down traffic through the Strait of Hormuz, the shipping channel through which one-fifth of the world’s daily oil flows. While Arab neighbors and allies like Russia and China have yet to offer Iran any concrete support, realists who spoke to the Sun express concern that proxies in Iraq and elsewhere in the region could be gearing for action.

America’s challenge at this point will be to avoid being drawn into a broader war requiring troops on the ground, a political scientist who favors realist notions of power dynamics and competition, Graham Allison, tells the Sun. He says that while Prime Minister Netanyahu’s objective is regime change, “that is not high enough in our hierarchy of U.S. interests to send Americans to fight and die on the ground for.”

“The fantasy of regime change is just that,” a professor of intelligence and national security at Texas A&M’s school of government, Christopher Layne, tells the Sun. “Yes, the mullahs’ theocracy may be overthrown or collapse. But it’s naive to think a successor government would be more friendly” to the U.S. and Israel. “Iranian nationalism won’t disappear even if the mullahs do.”

The United States is inextricably linked to Israel’s strategic goals toward Iran, a professor of international relations at Notre Dame and self-described “card-carrying realist,” Michael Desch, tells the Sun. “I don’t see how we can get away from a wider war.”

Other realists fear that the anti-American and pro-nuclear sentiment in Iran might only get stronger following the airstrikes, even as the country’s capabilities to build that power appear to be severely diminished.

“Helping Israel damage Iran’s nuclear infrastructure will only increase Iran’s desire to get a deterrent of their own,” a leading proponent of the realist tradition and a professor of international affairs at the Harvard Kennedy School, Stephen Walt, tells the Sun, “and guarantee a less stable region for many years to come.” 

As leading academic realist in the late 20th century, Kenneth Waltz, once put it: “the historical record indicates that a country bent on acquiring nuclear weapons can rarely be dissuaded from doing so.” 

Proponents of America’s attack on Iranian nuclear sites see it as squarely within the national interest. “Leaving Iran with a hardened nuclear enrichment facility after an Israeli military campaign would have been a recipe for maximum danger, all but asking Iran to sprint to a bomb,” the editorial board of the Wall Street Journal writes. It maintains that “Mr. Trump had to act to stop the threat in front of him to protect America, which is his first obligation as President.”

The most strident opponents of American engagement in the Israel-Iran war, including a mainstay of the MAGA base, hold a narrower definition of the national interest. They see intervention as the product of outdated ideology peddled by domestic interest groups and foreign lobbyists, with a media personality, Tucker Carlson, asserting that there was “zero credible intelligence” to suggest Iran was “anywhere near” building a nuclear bomb.

The realist school of thought, which overlaps with that of military restraint, contends that the leaders of even the most despicable regimes tend to act according to their own rational self-interest, bound by ambitions for global power, military prestige, and protection from attack. That philosophy posits that nations that acquire nuclear powers are bound by the precepts of rational deterrence. The alternative would be self-destruction. 

“Although the U.S. would prefer that Iran not get its own nuclear weapon, an Iranian bomb would not be a direct threat to the U.S. or to Israel,” Professor Walt says. “Why? Because Iran could not use it without committing suicide.”

Back in 2012, as America tightened sanctions on the Islamic Republic and debate raged over the best response to Iran’s nuclear activities, Mr. Waltz came to a similar conclusion. A nuclear-armed Iran, he argued in a 2012 Foreign Affairs article, “would probably be the best possible result: the one most likely to restore stability to the Middle East.”

Historical precedent suggests that nuclear powers are stymied from entering military conflict. In North Korea, the Kim dynasty sees nuclear weapons as the ultimate guarantee against foreign intervention. It began developing nuclear weapons with Soviet assistance in the 1950s and first successfully tested a nuclear device in 2006. 

Or take the case of China under Mao Zedong. He proclaimed in 1957 that nuclear war would ultimately lead to global communist victory. But once China became a nuclear weapons state, that kind of rhetoric quickly disappeared. “They never pursued the sort of nuclear overkill that the United States and the Soviet Union pursued at the height of the Cold War,” Mr. Desch says. 

Similar defensive thinking — along with grandiose visions of leading the Arab world — fueled the nuclear ambitions of Iraq under Saddam Hussein and Libya under Muammar Gaddafi, though neither nation succeeded in acquiring nuclear weapons. 

It was concerns of nuclear development (ultimately unfounded) that prompted President Bush to invade Iraq. And it was a desire for regime change that prompted American engagement in Libya and Afghanistan. If they have not learned from those “misadventures,” Mr. Desch says, perhaps the conflict in Iran today will finally shake off the hawkish instincts of the American political establishment. “I think Iraq and Afghanistan and Libya were, over the long term, a shot in the arm for the realism and restraint movement, because they went badly.”

A true realist, Professor Layne takes a pragmatic view of the way the American foreign policy pendulum is swinging. Before Sunday’s strikes, he proclaimed that “if President Trump involves the United States in Israel’s war with Iran, it will show that those arguing for a less interventionist U.S. role in the world have failed to win the intellectual debate on American foreign policy.”

“And that we still have work to do.”