Hundreds of thousands of federal employees are set to stay home without pay as of Monday morning following the dramatic collapse Friday night of talks to agree on an urgent funding measure.
The shutdown cast a huge shadow over the first anniversary of Trump's inauguration as president and highlighted the deep divisions between Republicans and Democrats.
Senate Majority Leader Mitch McConnell warned that the shutdown would "get a lot worse" if federal workers have to stay home without pay.
"Today would be a good day to end it," McConnell said from the Senate floor during a rare Sunday session aimed at hashing out a deal ahead of a vote he said would take place at 1:00 am (0600 GMT) Monday, unless progress is made sooner.
Lawmakers have traded bitter recriminations for the failure to pass a stop-gap funding measure, and McConnell once again sought to pin the blame on Senate Minority Leader Chuck Schumer.
Trump early Sunday encouraged the Senate's Republican leaders to invoke the "nuclear option" -- a procedural maneuver to change the chamber's rules to allow passage of a budget by a simple majority of 51 votes to end the shutdown.
"If stalemate continues, Republicans should go to 51% (Nuclear Option) and vote on real, long term budget, no C.R.'s!" he tweeted, referring to the stop-gap funding measure.
But Senate leaders have been wary of such a move in the past, as it could come back to haunt them the next time the other party holds a majority.
Undermining Trump's 'victory lap'
White House budget director Mick Mulvaney on Sunday accused some Democrats of wanting to "deny the president sort of the victory lap of the anniversary of his inauguration" -- echoing a complaint Trump made on Twitter the day before.
"There's other Democrats who want to see the president give the State of the Union during a shutdown," Mulvaney said on Fox, referring to the nationally televised address Trump is to deliver on January 30.
At the heart of the dispute is the thorny issue of undocumented immigration.
Democrats have accused Republicans of poisoning chances of a deal and pandering to Trump's populist base by refusing to back a program that protects an estimated 700,000 "Dreamers" -- undocumented immigrants who arrived as children -- from deportation.
Schumer said he and Democrats were willing to compromise, but Trump "can't take yes for an answer -- that's why we're here."
"I'm willing to seal the deal, to sit and work right now with the president or anyone he designates -- let's get it done," Schumer said.
Essential federal services and military activity are continuing, but even active-duty troops will not be paid until a deal is reached to reopen the US government.
There have been four government shutdowns since 1990. In the last one, in 2013, more than 800,000 government workers were put on temporary leave.
"We're just in a holding pattern. We just have to wait and see. It's scary," Noelle Joll, a 50-year-old furloughed US government employee, told AFP in Washington.
A deal had appeared likely on Friday afternoon, when Trump -- who has touted himself as a master negotiator -- seemed to be close to an agreement with Schumer on protecting Dreamers.
But no such compromise was in the language that reached Congress for a stop-gap motion to keep the government open for four more weeks while a final arrangement is discussed. And Republicans failed to win enough Democratic support in the Senate to bring it to a vote.
Republicans have a tenuous one-seat majority in the Senate, and on Friday needed to lure some Democrats to their side to get a 60-vote supermajority to bring the motion forward. They fell 10 votes short.
The measure brought to Congress would have extended federal funding until February 16 and reauthorized for six years a health insurance program for poor children -- a long-time Democratic objective.
But it left out any action on the Deferred Action on Childhood Arrivals program, known as DACA, that affects Dreamers.
White House officials insisted there was no urgency to fix DACA, which expires March 5.
Highlighting the deep political polarization, crowds estimated to number in the hundreds of thousands took to the streets of major US cities including Los Angeles, New York and Washington over the weekend to march against the president and his policies and express support for women's rights.
Protesters hoisted placards with messages including "Fight like a girl," "A woman's place is in the White House" and "Elect a clown, expect a circus."
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
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