Ukraine’s president, Volodymyr Zelensky, had good cause to be optimistic following his recent White House meetings with Donald Trump and the leaders of the European “coalition of the willing”. While a concrete peace plan has yet to emerge, Trump appears to have come around to the European position that security guarantees will be vital if any peace deal is to stick.

This is real progress. But what shape would security guarantees take in the case of Ukraine, and will they be enough to deter the Russian president, Vladimir Putin, from breaking the peace at some future date?

Talk of security guarantees is nothing new. Zelensky and his European allies have been stressing their importance for much of the conflict. But what does appear significant is the way in which the latest proposals have been framed.

It has been suggested that Ukraine should be offered security guarantees that resemble what Italy’s prime minister, Giorgia Meloni, called an “article 5 model”. This is a reference to the defence provision of Nato’s founding treaty, which specifies that an attack on one member is an attack on them all and requires a collective response.

Nato’s Article 5 is the gold standard of security guarantees. The wording is open to interpretation, but no one doubts that the principle of collective defence it embodies is the core purpose of the 32 nations which make up the alliance. Article 5 is backed by credible force that outclasses Russian military might.

Certainly, questions hang over article 5’s reliability. The provision has only ever been activated once – following the 9/11 attacks on the United States in 2001. But the unusual circumstances of that single invocation do not render the provision any less valuable.

The fact that European allies came to America’s........

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