As the war with Israel escalates, Ayatollah Ali Khamenei’s successor is already being discussed in some political circles.

In his many years as Supreme Leader of Iran, Ali Khamenei has gained a reputation for political caution; deep conservatism; and absolute ruthlessness. But above all, he is stubborn.

Faced with the killing of numerous members of his military high command, the destruction of swathes of the Islamic Republic’s treasured nuclear program and with enemy jets operating freely over his capital, he responded to Donald Trump’s demand for surrender this week by declaring: “The Iranian nation will stand firmly against any imposed war, just as it always has.”

“The Iranian nation also firmly stands against any imposed peace. The Iranian nation will not capitulate to anyone in the face of coercion,” the 86-year-old cleric went on.

It is fighting talk. But many believe it is at odds with reality. “It is becoming clearer every day that this is the beginning of the end of the regime in Tehran,” says Lina Khatib, visiting scholar with the Harvard Kennedy School’s Middle East Initiative.

“My crystal ball does not tell me how long it will take. But I do not see how the Islamic Republic – as it has been [for] over more than five decades – can survive this war.”

‘The $10 billion question’

Of course, it is not inevitable that Khamenei will fall.

But the decisive moment may come sooner rather than later. Trump on Thursday gave Khamenei a two-week deadline to make a deal to end its nuclear programme and defuse the crisis. At the end of the fortnight, the US president will make a decision about “whether or not to go” – in other words, to send American bombers to join the Israeli assault.