Pope Leo upholds Vatican opposition to nuclear weapons despite Trump's 'weak' critique

The verbal attacks from Trump on Leo this week come as the U.S. has launched thousands of missiles into Iran in a weeks-long war, which the president has sought to justify with an evolving list of rationales that has included preventing the Middle East country from developing a nuclear weapon.

Challenging Trump's social media characterization are the words of Leo himself, who has made a call for the disarmament of nuclear weapons a core tenet of his persistent pleas for peace since his papacy began 11 months ago, at times directly referencing Iran and the United States. While Trump too has expressed a desire for denuclearization, his public rebuke of the pope has brought to the fore starkly opposing views on how to achieve it.

"The pope is the one who is clear-eyed and understands the need for preventing Iran from getting a nuclear weapon, but also the appropriate means for pursuing that goal," said Gerard Powers, director of Catholic peacebuilding studies at the University of Notre Dame's Kroc Institute for International Peace Studies. "And the use of military force is not the appropriate means, probably because it's immoral and it's also likely to be counterproductive."

A peace of disarmament

Speaking from the balcony of St. Peter's Basilica, Leo began his papacy with the message "Peace be with you all!" framing it in part as "a peace that is unarmed and disarming."

Since then, the appeal for peace has emerged as a central tenant of Leo's young papacy, playing out as conflicts have erupted and exacerbated in Ukraine and Russia, Israel and Gaza, Sudan and now in Iran. Subsequent addresses and messages further linked the peace that Leo envisioned with a world free of threats of nuclear warfare.

Commemorating in July the 80th anniversary of the U.S dropping atomic bombs on Hiroshima and Nagasaki, Pope Leo called the two Japanese cities "living reminders of the profound horrors wrought by nuclear weapons."

"Indeed, true peace demands the courageous laying down of weapons — especially those with the power to cause an indescribable catastrophe," he said. "Nuclear arms offend our shared humanity and also betray the dignity of creation, whose harmony we are called to safeguard."

In his new-year message to the diplomatic corps to the Holy See, Leo pressed nations to renew the New START Treaty, the 2010 agreement between the U.S. and Russia, the world's top nuclear powers, that placed limits on each country's strategic nuclear weapon arsenals.

"There is a danger," Leo told diplomats in January, "of returning to the race of producing ever more sophisticated new weapons, also by means of artificial intelligence."

He repeated that message in February as the treaty expired and exhorted the U.S. and Russia to develop a follow-up mechanism to contain nuclear proliferation.

"In renewing my encouragement for every constructive effort in favor of disarmament and mutual trust, I urgently call for this instrument not to be abandoned without seeking to ensure its concrete and effective follow-up. The current situation requires that everything possible be done to avert a new arms race that would further threaten peace among nations," he said at the end of his general audience Feb. 4 in St. Peter's Square.

"It is more urgent than ever to substitute the logic of fear and distrust with a shared ethos capable of guiding choices towards the common good and to make peace a treasure to be cherished by all," the pope said.

Disagreement on deterrence

While Leo preached disarmament and for global leaders to abandon nuclear pursuits, the Trump administration has adopted a philosophy of "peace through strength" building up the country's military and nuclear capacity as a means to deter war. 

To that end, his administration has undertaken expansive plans to modernize and overhaul the country's nuclear arsenal, to an estimated cost of $946 billion over the next decade. Trump has suggested plans for a nuclear test and deployment of more weapons and also touted expanding nuclear energy. Trump, who has spoken of a goal to denuclearize, is seeking $1.5 trillion for defense spending for the 2027 budget, a 44% increase and the largest request in decades.

As of 2023, the U.S. Energy Department arsenal counted 3,748 nuclear warheads. 

Addressing the general conference of the International Atomic Energy Agency in September on behalf of the pope, Msgr. Daniel Pacho, an undersecretary for the Vatican's Secretariat of State, called the accumulation of nuclear weapons and overall rise in military spending "an affront to humanity as a whole, as a major nuclear confrontation would undoubtedly have an irreparable and devastating impact and result in unparalleled loss of human lives."

Leo has repeatedly rejected ramping up the machines of war as an effective means of deterrence. At times, he has turned to St. Augustine — the fourth-century doctor of the church who inspired the Augustinian religious order that Leo led from 2001-2013 — as another who challenged the view of peace through force.

"The idea of the deterrent power of military might, especially nuclear deterrence, is based on the irrationality of relations between nations, built not on law, justice and trust, but on fear and domination by force," the pope said in his message for the 2026 World Day of Peace (Jan. 1).

In his message marking the World War II bombings, Leo urged all countries to "reject the illusion of security founded on mutually assured destruction. Instead, we must forge a global ethic rooted in justice, fraternity and the common good."

Along with urging the U.S. and other nations to abandon their nuclear arsenals, Leo appeared to express concern with Iran acquiring its own in comments in June. 

As Israel and the U.S. bombed nuclear facilities and other strategic sites in Iran over 12 days that month, Leo lamented "the situation in Iran and Israel has deteriorated gravely" and appealed "responsibility and reason."

"The commitment to creating a safer world, free from the nuclear threat, should be pursued through respectful encounter and sincere dialogue, to build a lasting peace, based on justice, fraternity and the common good. No one should ever threaten the existence of another," the pope said.

Leo's approach to nuclear threats, including his criticisms of deterrence, is consistent with past popes and the Vatican's position since the end of the Cold War, said Notre Dame's Powers. "It's obviously an important issue to him. It's not like he's failing to address it," he said.

Coordinator of the Catholic Peacebuilding Network, Powers has worked on nuclear issues since the 1980s, including 17 years with the U.S. Conference of Catholic Bishops. He told NCR it was promising to see the pope's appeals for peace becoming front-page news at a critical time which he views as the greatest risk of a nuclear strike since the 1962 Cuban Missile Crisis. In January, the Bulletin of the Atomic Scientists placed its Doomsday Clock at 85 seconds to midnight, its closest position to date to global catastrophe.

"Everybody knows who pays any attention that the church is opposed to the use of nuclear weapons," he said. "The challenge is then to get the message out. And the message is now getting out, and really which we haven't seen in probably decades."