Fifteen years ago this fall, in the run-up to the invasion of Iraq, one of the most compelling public cases for war came not from President George W. Bush or his backers on Capitol Hill but from a wonky book written by a former C.I.A. analyst that landed, improbably, on best-seller lists and nightstands across Washington. Ken Pollack, now a scholar at the Brookings Institution, argued soberly but forcefully that a U.S.-led military assault to remove Saddam Hussein was necessary and affordable, what he called “our best option—or at least our least bad option.” The book’s title, “The Threatening Storm: The Case for Invading Iraq,” was less nuanced but more memorable than Pollack’s analysis, which acknowledged the risk of trading “the threat of a nuclear-armed Saddam for the threat of an Iraq in chaos and civil war.”

The book quickly became the intellectual foundation for proponents of the Iraq War, many of whom, unlike Pollack, knew nothing about Iraq. Democratic politicians found an excuse to avoid opposing the President, a year after the 9/11 attacks. Skeptics were forced to reckon with an expert endorsement of the Administration’s shoddy intelligence. Like the decision to invade Iraq, the book has not aged well.

These days, it is hard not to think back to 2002. Now, as then, a new Administration seems to have come into office with a Middle Eastern country in its crosshairs: this time, it is Iraq’s neighbor, Iran. Now, as then, a President is making increasingly menacing threats and politicizing intelligence to fit alternative facts. And now, as then, some of the same influential voices outside the Administration will play a crucial role in either legitimizing or discrediting decisions that risk another unnecessary and reckless war.

For the last decade, advocates of the Iraq War from both parties have worn scarlet letters around Washington but few have suffered professionally, even after “Mission Accomplished” turned into a brutal sectarian conflict that cost trillions of dollars, claimed the lives of more than forty-five hundred Americans and many times that number of Iraqis (most of them civilians), and badly damaged the United States’s moral and strategic authority in the world.

But several of the Iraq War’s most prominent proponents have experienced a renaissance of sorts after voicing early, principled, and fervent opposition to President Trump—whose populist rhetoric and isolationist views they found distasteful. As a group, they share right-leaning politics, hawkish foreign-policy views, and strong support for the invasion of Iraq—and they have, to their credit, emerged as some of the most unexpected and effective opposition voices.

David Frum coined George W. Bush’s infamous phrase “axis of evil,” in the speech that laid a predicate for war. Today his anti-Trump essays in The Atlantic are among the most trenchant and eloquent anywhere. Max Boot, of the Council on Foreign Relations, who wrote on the tenth anniversary of the Iraq War that its proponents had “no need to repent,” has relentlessly assaulted Trump’s dysfunctional management of national security on television, in print, and on Twitter.

William Kristol, the founder of The Weekly Standard, predicted, in 2003, that the Iraq War’s proponents would be “vindicated” by the discovery of weapons of mass destruction, and argued just two years ago that “we were right to fight in Iraq.” More recently, he has taken Trump to task for everything from his troubling ties to Russia to his mishandling of North Korea.

And Bret Stephens was the editor-in-chief of the Jerusalem Post when, in 2003, it named one of the Iraq War’s chief architects, Paul Wolfowitz, its “man of the year,” trumpeting his role as “principal author” of the doctrine of preëmptive war that would “underpin U.S. action against other rogue states.” As a longtime Wall Street Journal columnist, he continued to defend the evidentiary basis for war with Iraq long after it was discredited, but his attacks on Trump reportedly fell out of favor with the paper’s management, and he decamped earlier this year to the New York Times.

Today, these and other “Never Trump” Republicans have found common cause with the left-leaning anti-Trump “resistance,” who devour and distribute their media appearances with a fervor that would have seemed impossible pre-Trump. This alignment of convenience and conviction will face a severe test in the coming months, over the looming prospect of yet another potential conflict in the Middle East. These commentators share another common view: long-standing support for a more belligerent posture toward Iran, including military confrontation, regime change, or both.

Opposition to Trump among Iraq War proponents was always partly rooted in the President’s aversion to activism abroad. They have been right to decry Trump’s abdication of U.S. leadership, including his disregard for human rights, his belittling of our alliances, and his kowtowing to Vladimir Putin. But as a candidate, Trump’s stated suspicion of military adventurism, particularly in the Middle East, had been one of his most—of, arguably, few—rational foreign-policy stances. As President, however, Trump has escalated military action in Afghanistan, Iraq, Syria, Yemen, and Somalia, often without articulating a strategy and without public debate. In the case of Iran, while a formal policy “review” is still ongoing, Trump’s own proclivity for bluster, and apparent obsession with undoing whatever President Barack Obama did, is already leading in a dangerous direction.

Trump has long decried the nuclear deal with Iran as the “worst in history.” In July, he grudgingly certified to Congress that Iran is implementing the Joint Comprehensive Plan of Action—the formal name of the deal, from 2015, which degraded Iran’s nuclear program, and increased the amount of time needed to produce enough fissile material for a weapon to more than a year, in exchange for sanctions relief. But Trump also said, in July, that he believes Iran is not complying with the deal “in spirit.” In another echo of 2002, Trump has reportedly assigned a team to build a case against the deal, regardless of what the intelligence might indicate, and despite the fact that the rest of the world has concluded that Iran is honoring its commitments. International inspectors, as recently as Wednesday, have reiterated an opinion that is shared by Trump’s own State Department: that Iran is not violating the agreement.

There are many paths that Trump could take to deliver a blow to the nuclear deal and trigger a crisis with Iran. Two deadlines are looming this fall: in September, the U.S. must issue a waiver for sanctions suspended under the J.C.P.O.A.; in October, the U.S. has to certify that Iran is abiding by the agreement. Trump could decline to certify Iran’s compliance; re-impose sanctions that were suspended under the nuclear deal; dramatically increase sanctions on Iran for reasons unrelated to its nuclear program; or demand that monitors be allowed to visit sensitive Iranian military sites, in the absence of credible evidence of wrongdoing, a step that the U.S. Ambassador to the United Nations, Nikki Haley, threatened this week.

From there, the path to conflict, intentional or otherwise, is easy to imagine. Already, Trump has severed high-level diplomatic contact between the two countries, which is necessary to address misunderstandings and prevent small disputes from becoming large ones. Meanwhile, talk of promoting regime change in Tehran—among Republicans on Capitol Hill, in conservative Washington policy circles, and even from some Trump Administration officials—gives Iran’s already paranoid regime more justification to worry. If Trump imposes new sanctions, Iran could violate its commitments under the nuclear agreement. A clash between U.S. military advisers and Iranian fighters who are already operating in close proximity in Yemen, Iraq, and Syria could take place. Or, as has happened in the past, Iranian naval vessels could challenge U.S. warships in the narrow waterways around the Arabian Peninsula.