President Donald Trump's re-election coffers shrank in September as he fell behind Democratic challenger Joe Biden in the campaign money race, putting him at a disadvantage in the final weeks before November 3.
In a financial disclosure filed on Tuesday night with the Federal Election Commission, the Trump campaign said it had about $US63 million ($A89 million) in the bank at the end of September after spending about $US139 million that month.
A month earlier, the campaign reported having $US121 million in cash.
Biden's campaign has yet to report its cash holdings at the close of September.
However the former vice president's campaign said this month that together with the Democratic Party, it had $US432 million in the bank.
Trump and his Republican Party had just $US251 million, his campaign manager said this month.
Biden has held a significant lead over Trump in the national polls for months, although Reuters/Ipsos polling shows a somewhat closer race in the battleground states likely to decide the winner.
Trump has fallen far behind the Democrats in recent months at fundraising and spending.
Trump spent less than $US56 million on television and radio advertising in September, compared with nearly $US148 million by Biden, according to Advertising Analytics LLC, a market research company.
Including online ads, the president's campaign spent at least $US91 million on advertising in September, according to the disclosures filed on Tuesday.
Australian Associated Press
