Roughly twelve hours after he launched a war on Iran early on Saturday morning, President Donald Trump said his military campaign had killed the country’s supreme leader, Ayatollah Ali Khamenei.

“This is not only Justice for the people of Iran, but for all Great Americans, and those people from many Countries throughout the World, that have been killed or mutilated by Khamenei,” the president wrote on Truth Social.

But Trump’s effort to frame his war of choice as just and worthy of international celebration is a long shot. Instead, the administration’s latest military escalation is boosting a perception globally that could permanently and significantly hurt America’s and Americans’ role in the world: the view of the US as a rogue actor, fuelling instability, acting illogically and even illegally and risking innocent lives.

For all the questions remaining about the offensive – How long will it go on? Does the US have a plan to replace the regime if it falls? Is there any remaining hope for de-escalation? — a further degradation of America’s image abroad, including among its traditional allies, is one of few certainties.

“Even before today, the pattern was clear: this is a state that actively disregards international law and its protections for civilians, which makes civilians – makes children, makes pregnant mothers, make people who have nothing to do with geopolitical aims at all – less safe everywhere: in Gaza, in Canada, in Europe, in Asia,” said Mark Kersten, a professor at the University of the Fraser Valley in Canada. “Even in America itself, because international law is an important way to protect people in their own countries.”

Kersten characterised the new war as “unequivocally illegal… a wanton and clear violation” of the United Nations charter.

Trump began his offensive in Iran, in partnership with Israel, without even attempting to rally broader support from other countries or some legal basis for an attack through the UN Security Council, as former president George W. Bush did before the invasion of Iraq. He proceeded to assassinate Khamenei, who, while widely reviled, was a sitting head of state.

An anonymous US official eventually claimed to reporters that the U.S. acted preemptively in anticipation of an Iranian missile attack on American forces – but the administration has released no evidence of an imminent assault, experts see that prospect as very unlikely and another anonymous source contradicted the Trump administration’s claim to CNN. And the war represented the second time in less than a year Washington purported to be prioritising diplomacy with Tehran before choosing war.

Meanwhile, the administration has not offered any US plan to prevent a spiral of violence and atrocities in Iran and across the Middle East. A strike in the US-Israeli operation hit an Iranian primary school, killing more than 100 people, mostly schoolgirls, and throughout Saturday, Iranian retaliation struck neighbouring countries aligned with the US, wounding people and targeting civilian sites like airports and a hotel.

Given those facts, officials in the region and in Europe are alarmed, and their US counterparts are unlikely to be able to reassure them and encourage confidence in Trump’s strategy, said Jennifer Gavito, a former State Department official with senior roles across administrations of both parties.

“I look back to Libya and Iraq,” she said, referring to the chaos and mass death following American regime change missions in both countries. “I don’t know what reassurance could have been given in that moment – and especially with the benefit of history now on our side how you confidently project” success.”

Gavito noted public comments decrying the war from the foreign minister of Oman, which had sought to mediate between the U.S. and Iran: “It speaks to the betrayal that [other nations] feel that yet again we seemingly used negotiations as a cover and pretext for a strike that makes us in the future less of a credible partner.”

Reports suggest US and Israeli officials quietly planned the Iran campaign for months, even as Trump repeatedly said publicly that he wanted a deal.

The coming days and weeks are likely to bolster scepticism of the American strategy as Trump has offered conflicting visions of the resolution to the conflict, saying that he wants to see Iranian civilians abandon and topple the government and that he plans to continue bombing. A quick settlement on the core area of disagreement between Tehran and Washington – Iran’s nuclear and missile capabilities – is hard to imagine as a more hardline leadership is expected to succeed Khamenei and seek to project strength and resistance.

“We have already made this existential for the Iranian regime….so they have no incentive,” Gavito said. Already loath to make big concessions, Iran had reportedly this week offered greater limits on its nuclear development than it had in a previous nuclear deal with world powers, which Trump abandoned.

Waging a bloody, domestically unpopular and unauthorised war without a clear end, the Trump administration is unlikely to attract greater international backing.

Disdain rooted in the Iran policy will compound wariness of the US’s conduct and judgment in recent years in various contexts, from Trump’s kidnapping of Venezuela’s president last month to Gaza, in which Trump and before him President Joe Biden have defied calls to reconsider heavy American support for devastating Israeli policies decried by most countries.

“Coming after the Gaza war, where the US was seen in violation of international law and working against all human rights statutes by enabling Israeli genocide, we have now another instance by another admin of a different political view, confirming again that the US does not work according to international law,” said Randa Slim of the Stimson Center think tank. “The US is increasingly seen as a country that does not play by the book.”

To the Trump administration, its allies and others, global goodwill and legitimacy may seem irrelevant. Senator Lindsey Graham, a staunch proponent of attacking Iran and defender of Israeli conduct, on Saturday attacked European countries for suggesting the US should return to diplomacy with Tehran.

“It is so sad to see Western democracies lose their passion for justice and a sense of right and wrong,” Graham wrote on X. “You’re suggesting we should continue to negotiate with religious Nazis. It is pathetic.”

And Iran on Saturday also drew criticism from national security and legal analysts and other observers for its attacks on nearby countries, which had repeatedly said they did not want to see a war with their neighbor and attempted to overcome years of mutual distrust.

“These actions …set back years of rapprochement,” Slim said, noting Arab nations had recently come to see Israel’s heightened regional power as a greater threat but the risk posed by Iran was now “reemphasised.”

But with many people around the globe now wondering how US policy could unexpectedly spiral and harm them, Kersten described a heightened foreign focus on disconcerting Washington policy-making and the hope of changing it.

“Blatant threats to [Canada’s] sovereignty were in some ways a harbinger for how states can navigate [the Trump era] and I don’t think they have figured out how to navigate this,” he said, pointing to Canadian Prime Minister Mark Carney’s embrace of the attack on Iran despite his high-profile recent remarks urging countries to re-emphasise the importance of law and principles in international politics.

Kersten suggested foreigners are still searching for “voices of reason” in the United States, and feel dismayed by what they are seeing.

“If this dangerous path is to stop, it is only going to stop because of the actions of people within the United States,” Kersten said. “Canada can’t stop it . Middle Eastern partners have demonstrated they can’t stop it .. the UN will not. No international organisation or tribunal or coalition of states, whether [the European Union] or any other entity can.”