The upper chamber of Congress closed up shop late Thursday and reopened in the dark of night for a new session at 12:01 am Friday, launching a new effort to pass a bill to extend federal funding for six more weeks.
The Senate was expected to hold a vote on the measure at 1:00 am and, if it passes, send it to the House of Representatives and then on to Trump, who could quickly sign it and nip the shutdown in the bud.
But his administration had already prepared for a halt in operations.
The White House's Office of Management and Budget "is currently preparing for a lapse in appropriations," an OMB official said on condition of anonymity late Thursday, calling on lawmakers to get the measure to Trump's desk "without delay."
The bill, which includes a far-reaching deal that increases spending limits for the next two years and raises the federal debt ceiling until March 2019, would break the cycle of government funding crises in time for what is set to be a bruising campaign for November's mid-term elections.
The rebellion that simmered among Republicans and Democrats over the budget agreement boiled over when dogged Senator Rand Paul refused to allow the Senate to act expeditiously to pass the spending measure.
Moving legislation swiftly through the upper chamber of Congress requires consent by all 100 members, but Paul objected.
The Kentucky Republican took the floor to blast the increase in federal spending limits, and in particular the fiscal irresponsibility of his own party.
"I can't in all good honesty and all good faith just look the other way because my party is now complicit in the deficits," Paul said.
'Definition Of Hypocrisy'
"If you're against president (Barack) Obama's deficits, but you're for the Republican deficits, isn't that the very definition of hypocrisy?" he boomed, adding that he wants his fellow lawmakers "to feel uncomfortable" over the impasse.
Top Senate Democrat Chuck Schumer warned late Thursday that time was running short.
"We're in risky territory here," he said.
Senate rules dictate that Majority Leader Mitch McConnell can declare a new session at midnight, then hold a procedural vote on the spending bill one hour into the new day. A final vote would follow.
A McConnell lieutenant, Senator John Cornyn, took the floor late Thursday, and in a tense exchange with Paul asked for consent to move the vote up to 10:30 pm, then 11:00, 11:30 and midnight, in an last-ditch effort to avoid or at least minimize the shutdown.
"I don't know why we are basically burning time here," an exasperated Cornyn said. "We are in an emergency situation."
If passed early Friday, the bill would then head to the House, where the deal's fate is far from certain.
Fiscal conservatives in the lower chamber may join with Paul in balking at adding billions of dollars to the national debt two months after passing a $1.5 trillion tax cut package.
And liberal stalwarts including top House Democrat Nancy Pelosi were also in revolt because the deal does nothing to protect young undocumented immigrants from deportation.
$300 Billion More
House Speaker Paul Ryan appeared to shrug off concerns that several Republicans as well as Democrats might oppose the deal.
"I think we're going to be fine," he said in a radio interview about the looming vote.
The temporary spending bill under consideration incorporates the major budget deal reached between Senate leaders on both sides of the political aisle.
That agreement includes a $300 billion increase to both military and non-military spending limits for this year and 2019, and raises the debt until March 1 next year.
It also provides a massive $90 billion disaster relief package and funding to address the nationwide opioid abuse crisis.
Democrats have sought to link the federal funding debate to a permanent solution for hundreds of thousands of "Dreamer" immigrants who were brought to the country illegally as children.
Dreamers were shielded from deportation under the Obama-era program called Deferred Action for Childhood Arrivals (DACA). But Trump ended the program last September, setting March 5 as a deadline for resolving the issue.
The White House's current proposal -- one that would put 1.8 million immigrants on a path to citizenship, but also boost border security, and dramatically curtail legal immigration -- has been panned by Democrats.
Several bipartisan efforts have stalled.