The ongoing U.S. war against Iran, which kicked off in late February with the killing of more than 100 Iranian schoolchildren, has undermined a key State Department foreign policy tool and may have irreparably damaged the nation’s global reputation, a former Obama administration public diplomacy chief warned Sunday.

“I believe because of [President] Donald Trump and his war in Iran, American popularity will descend to depths it has not seen this century and may never recover to the median levels that we saw with Jimmy Carter and Ronald Reagan,” wrote Richard Stengel, former State Department under secretary for diplomacy, in an analysis published Sunday in The Guardian.

“Forget Barack Obama numbers – they’re out of reach. Confidence in Trump’s ability to navigate global affairs was already around 30-40% before the invasion of Iran. That will be the new ceiling.”

Stengel described his former job as being the United States’ “chief marketing officer of ‘Brand USA,’” with among his chief missions being to “help shape and promote America’s image abroad.”

With Trump having launched a war against Iran, however, one that has been condemned by America’s allies as unlawful, the United States’ ability to project “soft power” through fostering cultural influence abroad may have finally come to an end, Stengel warned, and largely due to Trump.

“Since Woodrow Wilson, American presidents have been in the democracy promotion business. That era may now be over,” he wrote.

“With the war on Iran, US action in Venezuela, and increasingly bellicose talk about Cuba, the Trump administration is reviving the old trope of the Ugly American, but this time without the once obligatory paeans to democracy. That old image of America as a narcissistic and culturally insensitive bully is back with a vengeance.”