Conflicts between political leaders and religious authority have shaped Western history for centuries – and continue to define debates over power and legitimacy today.

Alarm over the war of words between President Donald Trump and Pope Leo XIV has escalated with remarkable speed, from The New York Times to the Daily Beast and local television.

The pope has repeatedly called for peace in the Middle East since the start of the Iran war, insisting that “God does not bless any conflict” and warning against the “delusion of omnipotence.”

On April 12, in a lengthy social media post, Trump derided Leo as “WEAK on Crime, and terrible for Foreign Policy,” telling him to “focus on being a Great Pope, not a Politician.” His Truth Social account posted, then deleted, a Christ-like image of Trump appearing to heal a man.

At stake in this public feud is an old question: Can a religious leader challenge political power, especially a ruler of one of the most powerful countries in the world?

As a medieval historian and lead editor of The Cambridge History of the Papacy, I cannot help but see a familiar pattern.

For many people, Trump’s rant against the pope was shocking. But conflicts between popes and rulers are not an aberration; they’re a durable feature of western history. Whenever political leaders cloak power in sacred language, or religious leaders publicly denounce political violence, they reenact debates that stretch back more than a millennium. These struggles are not symbolic: They concern who holds ultimate authority over people, souls – and in the end, history itself.

From its earliest centuries, Christianity was bound up with politics. Roman Emperor Constantine legalised the religion in 313. He later presided over the Council of Nicaea, an........

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