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 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 it would work or be funded – saying only that the money would have to be spent in the US. Vice-President JD Vance has linked the plan to the revenue that Trump has raised for the US government using tariffs.Democrats labelled it an “empty promise” and others questioned whether such a pledge was legal or feasible.It may be the first time a US president offered such a payout to Americans, in the context of an election year plea to get out and vote.The idea drew raucous applause at the convention and Trump seemed to relish the moment.There are nearly 270 million American adults, meaning a $5,000 payout would cost the US government some $1.3 trillion.Questions have begun to be raised about whether his plan is feasible – especially as prices rise in the US, partially as a result 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, through which about a fifth of the world’s oil and liquefied natural gas used to transit.The blockage has caused fluctuations 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.Trump’s long speech at the Republican convention in Dallas, Texas, touched on the core of the conflict – the impact on Americans’ standard of living. His pledge to increase their spending power drew raucous applause in the hall.“If the Republicans win the House of Representatives and the United States Senate, both of them,” Trump said, “I will issue a dividend to every adult citizen in the United States of America for $5,000.”“We don’t want you going to Canada to spend the money,” he said.“We don’t want you going to China, to Germany. You got to spend the money in the United States of America.” It is not clear how the spending would be monitored.The BBC has asked the White House for further clarification on how Trump’s plan would work.It is not the first time that Trump promised such payouts – he has previously proposed $2,000 cheques to be funded by tariff revenues.Vice-President JD Vance indicated that these post-election payments could similarly be made possible by the money Trump has raised using his wide-ranging tariff programme.“What the president is talking about is fundamentally a dividend for American workers,” Vance told Fox News.“We’re taking in an extraordinary amount of revenue because the president of the United States is actually standing up to both foreign companies but also foreign countries who’ve been taking advantage of America’s workers.”Vance went on to say: “I don’t think it’s a controversial idea.”