Trump has clashed with Leo on everything from Iran to immigration and recently dismissed the pontiff as “weak” in an unprecedented personal attack on a pope by a US leader.
Leo, who was born in Chicago, has said he has a moral duty to speak out against war.
“For an ignoramus like Trump to try to question the theological outlook of an ordained priest is totally ridiculous,” Jim Supp, 88, told AFP outside a church in New York City on Friday.
Supp was particularly angered by Trump’s recent posting of an AI-generated image seemingly depicting himself as a figure like Jesus Christ, which was later deleted.
“There are certain things in life not to joke about,” said the retired classics professor.
For 68-year-old John O’Brian, a former advertising executive, sharing the image was akin to “blasphemy for Christians”.
The pope, for his part, has warned of the dangers of AI abuse following Trump’s post – without directly referencing it.
‘Don’t mess with him’
Traditionally, US presidents have been wary of upsetting American Catholics by speaking out too much against a pope.
But Trump has taken no such caution, despite winning the 2024 election with support from a majority of Catholic voters.
The war in the Middle East has proved a pinch point, with Leo condemning the president’s threat to attack Iranian civilization as “unacceptable”.
Trump retaliated by calling the pontiff “WEAK on Crime, and terrible for Foreign Policy.”
The public sparring marks a potential vulnerability for Republicans ahead of November’s midterms – even among more conservative Catholics.
Anthony Clark, a policy fellow with an anti-abortion group, told AFP outside a Catholic basilica in Washington that he sees Trump as a “very good president” with good intentions.
“But I think that intentions aren’t everything, and I think he can be imprudent at times in what he says or in the way that he approaches especially controversial topics,” the 20-year-old added.
Popes, too, typically do not interfere in politics. However, the pontiff’s defiance has earned him respect from some.
“I’m really glad that Pope Leo stood his ground when he said he’s not afraid of the administration,” Carolina Herrera, 22, said in Washington.
“You should not mess with the pope, no matter what, don’t mess with him.”
‘Very harsh’
Trump himself is not known to be personally religious. The thrice-married realtor and former television celebrity was raised Presbyterian and rarely attended religious services.
But since entering politics he has embraced the Christian right.
Christian conservatives have hailed Trump for helping them achieve their priority – the end of the nationwide right to abortion, thanks to justices Trump appointed to the Supreme Court.
At a church in Houston, in the Republican heartland state of Texas, some attending midday mass faulted both the president and the pope.
“I don’t think either of them are acting the way they should be acting,” said Ann, a white woman in her 70s who did not want to share her last name.
“I think [the pope] has been very harsh on America,” she added.
Meanwhile, Trump’s staunchest supporters rallied behind the president as they waited to see him address an event held by right-wing Christian group Turning Point USA at a Protestant megachurch in Arizona.
“I think that the pope needs to stay in his lane and I disagree with his accusations,” Brenda Gifford told AFP, adding, “I don’t respect him anymore.”
Armando Azpeitia, another Trump follower, had a more nuanced take on the papal tensions – even if she still sided with the president.
“I do see how he can disagree with some of the things that Trump says, but overall I still think that [Trump] has the best interests of the American people in his heart,” he said.