US President Donald Trump has offered every adult American $5,000 (£3,700) if Republicans win November's midterm elections, but it is unclear how such a plan would be funded and whether it is legal.

His remarks prompted raucous applause from supporters at a party convention on Wednesday night, although Democrats labelled it an "empty promise".

Trump also told the Republican conference that the money would have to be spent in the US, but it is unclear how that would be monitored.

US Vice-President JD Vance suggested it might be paid for by tariff revenue and that such cheques would not go to wealthy Americans.

Under US federal law, it is illegal to give payments that are intended to influence the way a person is voting.

However, some experts have said the offer made by Trump in Texas on Wednesday could be seen as a pledge to cut taxes, which is legal.

Dr Joan Mahoney, lecturer in law at the University of Southampton, told the BBC she thought the offer would be legal, though she said politicians "don't usually do it quite this explicitly".

"On the one hand it sounds a bit like a bribe, vote for the Republicans and you'll get money, which would be decidedly illegal," she said.

"But on the other hand it would go to everyone, regardless of how they voted so it isn't in that sense a bribe.

"I think it would be legal. It's the same kind of campaign pledge as saying 'if my party wins we'll reduce taxes'. Every party does that all the time… and that's obviously perfectly legal."

However, Laurel Rapp, director of the US and North America programme at Chatham House, told the BBC that Trump's offer seemed to be "a very different, very transactional agreement" from the kind of promise usually made by candidates in an election period.

Aside from the question of legality, some have also asked whether Trump's offer would be feasible financially in the context of increasing US debt, partially as a result of the war in Iran.

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

Trump gave no details on how such cheques would be funded.

Congress authorises spending in the US, but the president did not say whether he planned to ask for legislative approval for any payments.

And legal experts said it was unlikely he could approve such a vast sum via a presidential executive order.

Erica York, a senior economist at the Washington DC-based Tax Foundation, told the BBC she would be "extremely surprised" if Congress approved any proposal.

"This would be one of the worst ways to use $1.3 trillion," she said.

"We're on a very unsustainable track, with deficits only projected to grow and grow," York added.

Speaking to Fox News after Trump's speech, Vice-President Vance indicated that the payments could be funded by money raised by the president from tariffs.

However, such revenue to date falls far short of the money that would be needed to account for Trump's $5,000 cheques offer.

According to the Bipartisan Policy Center, the US has brought in around $475bn in tariff and excise tax revenue since the beginning of 2025.

But more than $100bn has been refunded after the Supreme Court struck down many tariffs earlier this year.

When asked how the payouts could work, the White House said in a statement to the BBC: "The doomers and naysayers have consistently doubted President Trump."

"With the continued support of the American people, President Trump will keep delivering real results," added spokesman Davis Ingle.

One former Republican strategist and pollster said Trump's latest offer should be firmly seen in the context of an election that is now less than two months away.

"It is an extraordinary promise, and I'm not sure where that money is going to come from – but it is campaign season," Robert Moran told the BBC.

Chatham House's Rapp said Trump was thinking short term to try to keep hold of Congress as he enters the final two years of his term in office.

"Money is something that he is now resorting to because the polling is not looking good for Republicans and the polling is not looking good for him," she continued.

Trump has previously proposed $2,000 cheques to be funded by tariff revenues, but those payouts have not materialised.

Former President Joe Biden was accused of buying votes when he promised $2,000 Covid stimulus cheques for Americans if Democrats won Senate elections in Georgia in January 2021.

A similar controversy arose ahead of the 2024 presidential election, during which billionaire Trump supporter Elon Musk offered cash incentives to registered voters in seven swing states who signed a certain petition.

Additional reporting by Bernd Debusmann Jr, White House reporter