Washington DC – Donald Trump attacked Pope Leo XIV on social media after the pontiff met with Chicago Mayor Brandon Johnson, one of the president's political rivals.

"Someone should explain to the pope that the mayor of Chicago is useless, and that Iran cannot have a nuclear weapon!" Trump raged in a Truth Social post on Saturday.

His outburst was supplemented by screenshots of posts by Johnson to X, specifically a series of images showing off the mayor's meeting with Pope Leo.

"Joining our Chicago faith community and his holiness, Pope Leo XIV, for a multi-faith prayer at the Vatican, yesterday, was one of the most awe-inspiring and humbling experiences of my life," Johnson wrote alongside the images.

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Johnson has been a tough critic of the Trump administration, voicing strong opposition to its use of masked US Immigration and Customs Enforcement agents to abduct people off the streets.

In February, he ordered Chicago's police force to investigate any illegal activity undertaken by federal immigration agents, declaring that "nobody is above the law" and his government is "putting ICE on notice."

On numerous occasions, Johnson has stood beside Illinois Governor JB Pritzker in opposition to Trump. At one point, he angered Trump to the extent that the president called for him to be arrested.

Trump has also been in a deep and ongoing feud with Pope Leo XIV, especially over the US leader's decision to launch a war against Iran.

In a follow-up post, Johnson shared Trump's attack on Leo and wrote that "Chicagoans have had enough of Trump's blasphemous war in Iran."

"Someone should explain to the president that his belligerence is only making it harder for working families to make ends meet," the mayor said.