US President Donald Trump has built a potential off-ramp by suggesting the Iran war could end soon, but the world is still guessing about whether he will take it – and whether Tehran will let him.

With surging oil prices threatening the global economy and his political fortunes at home, Trump’s tone appeared to shift abruptly on Monday as he called the war “very complete” and a “short-term excursion”.

But the 79-year-old commander-in-chief continued to send mixed messages about when the war could end – and what its goals are – leaving it far from clear what he will ultimately settle for.

For Trump, that calculation will almost certainly involve November’s US midterm elections, with fuel prices likely to fuel voter anger at his Republican Party over the cost of living.

Polls so far show historically low support among Americans for the war.

“I think he’s going to keep going until his advisers tell him that the economic pain is going to risk the midterms,” said Colin Clarke, executive director of the Soufan Centre in New York. “He’s going to make a political decision about a military operation.”