US President Donald Trump has threatened a “very long” government shutdown if Democrats do not fund his long-promised border wall.
In a series of tweets on Friday, Mr Trump demanded $5bn (£4bn), which was approved by the House but is expected to fail in the Senate.
“Shutdown today if Democrats do not vote for Border Security!” he tweeted.
If no deal is reached, parts of the US government will begin to close at midnight on Friday.
The partial shutdown would be the third such closure of federal agencies in 2018.
If it occurs, it may not be settled until after the New Year, when Democrats take control of the House of Representatives.
The Republican president has meanwhile irked members of his own party in the Senate by ordering a US troop withdrawal from Syria.
What did Mr Trump say?
In early morning tweets on Friday, Mr Trump accused Democrats of “trying to belittle the concept of a Wall, calling it old fashioned”.
“The fact is there is nothing else’s that will work, and that has been true for thousands of years. It’s like the wheel, there is nothing better,” Mr Trump wrote.
“In Israel the Wall is 99.9% successful,” he added. “Will not be any different on our Southern Border!”
“If the Dems vote no, there will be a shutdown that will last for a very long time. People don’t want Open Borders and Crime!”
Mr Trump – who will postpone his holiday in Florida in the event of a shutdown, aides say – urged Senate Republican leader Mitch McConnell to invoke the so-called “nuclear option”.
What is the ‘nuclear option’?
It would allow the budget to pass by a simple majority of 51 votes, rather than the 60 votes currently required under Senate rules.
The president’s fellow Republicans currently have 51 seats in the 100-seat Senate.
But Mr McConnell has repeatedly refused in the past to invoke such an extreme legislative manoeuvre.
Pundits say the “nuclear option” would politically inflame an upper chamber that prides itself on comity.
What happens if the government closes?
Roughly a quarter of the federal government – including the departments of Homeland Security, Transportation, Agriculture, State, and Justice – will shut down at midnight on Friday if no deal is reached.
National parks and forests will be closed.
But federal programmes on pensions and healthcare will continue to function, as will the military, border patrol, coast guard, federal judiciary, air traffic control and airport security.
The US Postal Service, which is delivering millions of packages before Christmas, will also be unaffected as it is an independent agency.
Federal workers who are deemed “essential” will also remain on the job, but will not receive a pay cheque directly before the Christmas holiday.