The former Central Intelligence Agency director John Brennan has added his name to growing calls for the president to be ousted on grounds that he is unfit for the job, arguing that the US constitution’s 25th amendment addressing involuntary removal from office was “written with Donald Trump in mind”.

Brennan, who served as head of the spy agency during Barack Obama’s presidency, told MS Now on Saturday that Trump’s recent volatile remarks about destroying Iranian civilization and the danger he posed to so many lives merited his removal from the Oval Office.

“This person is clearly unhinged,” he said. “I think the 25th amendment was written with Donald Trump in mind.”

Brennan added that Trump was too much of a liability to be allowed to continue to be commander in chief. He had immense firepower at his disposal, including the US nuclear arsenal.

The ex-CIA director’s comments casts him at the forefront of a mounting debate over Trump’s decision to go to war with Iran and his increasingly violent threats to inflict mass destruction on that country. On 7 April, the president warned that Iran’s “whole civilisation will die tonight” if the Iranian regime failed to meet his ultimatum – a threat which Brennan said hinted at the deployment of nuclear capabilities.

As Trump has ramped up his aggressive and expletive-filled rhetoric, an increasing number of Democrats have responded by calling for the 25th amendment to be invoked. The measure, baked into the US constitution in 1967, allows for the vice-president and a majority of the cabinet to remove the president on the basis that he is “unable to discharge the powers and duties of his office”.

More than 70 Democrats in Congress have called for the amendment to be applied, according to the latest count by NBC News.

The chances of that actually happening are close to nil, given the lock-tight loyalty that continues to be shown to Trump by his Vice-President JD Vance and his entire cabinet. However, concern about Trump’s increasingly charged language and dystopian threats are likely to persist given the failure of peace talks between the US and Iran on Saturday as well as the possibility of renewed hostilities.

Brennan’s comments were especially striking given that he is under active investigation by Trump’s US justice department as part of the president’s vendetta against his perceived enemies. Under pressure from the White House, the justice department put Brennan and the former FBI director James Comey under criminal investigation in July.

Two months later, Comey was charged with two counts accusing him of lying to Congress during testimony in 2020 over the Russia election interference investigation. A judge has thrown out that prosecution.

It is understood that the investigation into Brennan is ongoing. In March, the chair of the House judiciary committee, Trump ally Jim Jordan, claimed the inquiry was “heating up”.