US President Donald Trump says he would offer every adult American a $5,000 (£3,700) payout if Republicans win both chambers of Congress in November’s midterm elections – a plan that would cost more than a trillion dollars.

The controversial offer was made in a speech at the party’s first-ever convention in the middle of a US presidential term.

He gave no details on how the plan would work or where the money would come from – saying only that the money would have to be spent in the US.

Democrats quickly labelled it an “empty promise” and others questioned whether such a pledge was legal.

There are nearly 270 million American adults, which means a $5,000 payout would cost the US government some $1.3 trillion.

Questions about whether his plan was possible have started to be asked – especially as prices rise in the US – partially as a result of the consequences of the war that the US and Israel started with Iran in February.

Iran’s retaliation has included attacks against US bases and allies in the Gulf – but crucially it has largely closed the Strait of Hormuz where about a fifth of the world’s oil and liquefied natural gas used to transit.

The blockage has caused fluctuation in oil prices worldwide and Trump has faced pressure from his party to end the war.

On Wednesday, the US president warned his supporters that the war would not end until after the midterms and that oil prices would not come down until then.

He made the comments ahead of his speech in Texas, repeating it at the convention where he argued that short-term economic pain was worth it to prevent Tehran from developing nuclear weapons.