To the world, it has seemed clear for months that President Trump has been fighting with Pope Leo XIV about the U.S.-Israeli war in Iran, which the pope has said is not a just war.

But to the president’s man at the Vatican, that narrative is simply “false,” and “entirely unfair.”

In fact, the U.S. ambassador to the Holy See, Brian Burch, would go so far as to say that the pope — the first born in the United States — has not even declared the war unjust.

“The Vatican has not said, nor will they say, declare definitively whether or not this is a just or unjust war,” he said during a 90-minute interview from his office in Rome in late June.

Yet on a flight to Spain several weeks earlier, the pope spoke plainly.

“I believe this has already been made very clear: In Iran, the criteria for a just war are not present,” Leo said.

To Mr. Burch, declaring the Iran war unjust is not a judgment the pope can make because he has access to only “a set of limited facts.”

An ambassador’s job is always part ceremony, part policy. Inevitably, there are differences between countries that the diplomat must help navigate.

But Mr. Burch is in an unusual spot. Leo is no typical head of state who deals simply in temporal politics. He is the world’s most prominent religious leader, attending to the moral lives of 1.4 billion Catholics, including Mr. Burch.

A longtime conservative Catholic activist, Mr. Burch also navigates the relationship between the two most prominent American men in the world — a popular pope and a bellicose president who have sharply diverging visions of global leadership.

“I have never once thought for a second that somehow I couldn’t properly represent the president,” Mr. Burch said, adding that he believes the president and the pope share goals that “are very much aligned.”

An American pope is a unique opportunity for the United States, but he said that fundamentally, “the policies and leadership of President Trump are enabling a moment for the Catholic Church to both grow and thrive.”

At times, Mr. Burch believes the Vatican has failed to understand Mr. Trump’s agenda. After the Defense Department invited Cardinal Christophe Pierre, the Vatican’s ambassador to the United States at the time, to a rare meeting at the Pentagon in January, reports spread that U.S. officials had threatened the Vatican for its position on the war in Iran. The meeting was “grossly mischaracterized,” Mr. Burch said.

Mr. Burch presumed a leak had likely come from the Vatican’s side — “the story was largely an attack on the United States,” he said — so he called Cardinal Pierre to ask for an apology and to help identify “who was lying about this meeting,” he said. He then posted a statement saying that Cardinal Pierre “emphatically denied” the reports, and the Vatican also confirmed that details of the meeting had been exaggerated. Cardinal Pierre did not respond to a request for comment.

Mr. Trump nominated Mr. Burch, who had been the president and co-founder of Catholic Vote, a political advocacy group, after he successfully helped him win key states like Pennsylvania in the 2024 election. Mr. Burch’s confirmation as ambassador was a symbol of the rising strength of the conservative Catholic movement in America. He and his wife have nine children, and like Leo, he lived in the Chicago area.

Mr. Burch’s views on the president have evolved over time. Catholic Vote did not support Mr. Trump in 2016, citing concerns over his moral judgment, but it had reversed course by 2020. In Mr. Burch’s book “A New Catholic Moment: Donald Trump and the Politics of the Common Good,” he wrote, “Donald Trump is Catholics’ best choice — perhaps our only choice.”

Over the course of two interviews in the past two weeks, Mr. Burch sometimes deployed his own Trump-like rhetorical flourishes.

“This is such a mischaracterization that somehow the president seeks war,” he said. “The last thing the president wants to do is go to war.”

He said the pope and the president did not disagree “on what needed to be done” in Iran. “The disagreements we have is often not over ends, but over means,” he said. “And often not just means, but on pace.”

Mr. Burch saw Mr. Trump’s social media outburst as an example of the president “negotiating” to “secure the support of the Holy See around his efforts to protect the world from nuclear catastrophe.”

But at a time when the pope is one of the few world leaders who can openly criticize the president without fear of economic or military reprisals, Mr. Burch also suggested that the president wanted the pope’s moral approval.

“When the Holy Father speaks, people pay attention,” he said.

Mr. Burch said that even if the pope declared the war unjust, he didn’t mean it.

“You’re right, he did say that,” Mr. Burch later said, referring to the pope’s statement about the Iran war.

He continued: “But keep in mind the ‘just war’ tradition for the Holy See does rely ultimately upon the prudential wisdom of the legitimately elected sovereign” of a country that wages war.

Mr. Burch argued that when the pope spoke out against the war, he was not doing so as the leader of the Roman Catholic Church, the vicar of Christ, but only as the sovereign political leader of the Vatican City-State.

“When the pope acts as the sovereign leader of the Holy See, he is coequal with world leaders,” he said.

Unlike many other world leaders, Mr. Trump has not yet visited the Vatican. And, as far as Mr. Burch was aware, the president has yet to speak directly with the pope, via phone or text or otherwise. The only known letter Mr. Trump has sent to Leo was the official presidential introduction that Mr. Burch presented to the pope when confirming his credentials, he said. Mr. Vance and Secretary of State Marco Rubio have both met with Leo at the Vatican.

Mr. Burch argued that the pope typically doesn’t directly engage leaders in “the traditional way that say Trump calls Putin.”

“I don’t know, how many conversations has the pope had with Giorgia Meloni directly?” he said, referring to the Italian prime minister. The pope and Ms. Meloni have met and spoken on the phone more than once, and the pope has hosted 82 world leaders, including President Emmanuel Macron of France, Prime Minister Donald Tusk of Poland and President Javier Milei of Argentina. He has also spoken by phone with other leaders, including the prime ministers of Canada and Israel, Mark Carney and Benjamin Netanyahu, and the president of Ukraine, Volodymyr Zelensky.

Meanwhile, Mr. Burch tries to push the president’s mission at the Vatican, even if he is sometimes out of the loop.

He first learned that the president had attacked the pope on social media in April just as everyone else did, when alerts popped up on his phone. The pope was on his way to an 11-day trip to Africa and Mr. Burch texted the Vatican’s foreign minister, Archbishop Paul Gallagher, offering to explain U.S. policy. (Asked if he also reached out to the White House after Mr. Trump’s outburst, Mr. Burch changed the subject. Archbishop Gallagher’s office did not respond to a request for comment.)

Mr. Burch said he met with another official in the Vatican’s Secretary of State’s office to express the U.S. government’s concern that the media had interpreted many of the pope’s words during his trip as criticism of Mr. Trump. Leo soon clarified publicly that he was not exclusively referring to the president.

Mr. Burch also suggested that the pope’s criticism of the United States was disproportionate to his criticism of human rights violations elsewhere, including in China.

“The Vatican has felt very comfortable reminding the United States of its moral obligations,” he said. “And certainly we would welcome the Holy Father to be very public and forthright about the obligations that China has to its own people.”

So far, Leo is handling the country of his birth on his own terms. On Saturday, the 250th anniversary of the Declaration of Independence, Leo visited Lampedusa, the tiny Mediterranean island that has become a gateway to Europe for asylum seekers, to show support for migrants after declining an invitation from the White House to join the festivities in Washington. He also sent a letter directly to the American people, congratulating them and reminding them that “defending human life also includes welcoming, protecting and assisting immigrants.”

In what appeared to be a conciliatory gesture from the pope and a diplomatic coup for Mr. Burch, Leo joined Mr. Burch and his family for a rare private dinner at the ambassador’s residence in Rome on the night the pope returned from Lampedusa. The Vatican did not offer a readout of the dinner, but Mr. Burch described it as a “reminder of the closeness of our two nations.”

He added: “We had an encouraging dialogue on President Trump’s bold leadership.”

Josephine de La Bruyère contributed reporting