Pope Leo XIV and Giorgia Meloni should take comfort from the fact that the main thrust of Donald Trump's attack on them contains a clue as to how peace can be restored between Iran and the United States.

By alleging that their opposition to his war means that the Pope and Meloni must be happy for Iran to possess a nuclear weapon (and even to attack Italy with one) Trump has shown that he is now reframing the war's purpose as being chiefly about nukes rather than regime change or anything else.

Moreover, this retrospective reframing, made at the risk of alienating many of America's estimated 53 million Catholic voters, indicates that he hopes that Iran can now be forced to agree to constraints on its nuclear program, allowing him to declare a sort of victory.

This outcome is possible, but to achieve it he will probably have to get help from China. And his negotiators will have to borrow from the work of some of the people he hates most: Barack Obama and the governments of Germany, France and the United Kingdom.

Nuclear weapons will not be the only determinant of whether Iran and the United States can renew their ceasefire which expires on April 21st and come to a peace agreement. Other issues on which the two sides remain apart include

the terms by which the Strait of Hormuz can be managed in future;

the American, European and other western sanctions on Iranian exports, foreign assets and financial institutions;

Iranian support for the violent militant groups of Hizbollah in Lebanon, Hamas in Gaza and the Houthis in Yemen; and

the future of Iran's ballistic missiles program.

But Trump's recent highlighting of nukes suggests that this may be the key that can unlock the rest of the deal, at least from his point of view.

Let us be clear: no one is in favor of more countries than the current nine – America, Russia, China, India, Pakistan, Britain, France, Israel and North Korea – possessing nuclear weapons. The question is: What can and should be done to prevent anyone else from joining the nuclear club?

The historic answer has been the Nuclear Non-Proliferation Treaty of 1968, under which both nuclear and non-nuclear states made commitments to prevent the further spread of weapons technology while allowing and managing the sharing of peaceful nuclear-energy technology.