‘Of course there’s going to be retaliation,’ says one expert. ‘It may be that this is what Trump’s interested in’

For decades, the US and its allies have painted Iran as the world’s biggest sponsor of state terrorism – invoking its Islamic rulers’ supposed revolutionary fanaticism and determined support for militant proxies.

Now a long-standing but mainly latent threat is coalescing, with the war waged on the country by the US and Israel, to raise the risk of an attack on American soil to levels unseen since the murderous al-Qaida assaults of 11 September 2001, experts say.

In an election year, opponents of Donald Trump are warning that such an event could rebound to his advantage – providing him with a pretext to crack down on critics by declaring a state of emergency or even cancelling November’s congressional midterm elections.

Two attacks on Thursday alone illustrated the heightened dangers.