US President Donald Trump has said he is ending negotiations over a Covid-19 relief bill, and will only resume talks after the election.
He predicted he would win next month's election and pass a bill afterward. US stocks fell after the announcement.
Budget talks between Democratic Speaker Nancy Pelosi and Treasury Secretary Steven Mnuchin began in July.
Democratic presidential nominee Joe Biden said Mr Trump had "turned his back" on the American people.
"Make no mistake: if you are out of work, if your business is closed, if your child's school is shut down, if you are seeing layoffs in your community, Donald Trump decided today that none of that - none of it - matters to him," Mr Biden said in a statement on Tuesday.
The Republican president - who is himself currently being treated for Covid-19 - countered: "Crazy Nancy Pelosi and the Radical Left Democrats were just playing 'games' with the desperately needed Workers Stimulus Payments.
"They just wanted to take care of Democrat failed, high crime, Cities and States. They were never in it to help the workers, and they never will be!"
He said he had instructed Republican Senate Majority Leader Mitch McConnell to focus efforts on confirming his Supreme Court nominee Amy Coney Barrett.
McConnell later told reporters he supported the president's move because he believed a deal with the Democrats was looking too difficult. "We need to concentrate on the achievable," he said.
Lawmakers from both parties had hoped for another round of Covid-19 relief spending to pass ahead of the 3 November election, but President Trump's tweet appears to have abruptly suspended that prospect.
It comes as coronavirus cases rise in several parts of the country, the outbreak widens among White House staff and Republican senators, and hits Pentagon top brass.