WASHINGTON (AP) — Bleary-eyed lawmakers worked through a mountain of amendments Saturday as the Senate plodded toward passage of a $1.9 trillion COVID-19 relief bill that President Joe Biden and Democrats say is crucial for hoisting the country out of the pandemic.

The Senate commenced a dreaded “vote-a-thon” — a continuous series of votes on amendments — shortly before midnight Friday, and by midmorning Saturday had dispensed with over two dozen. Democrats were hoping for final passage by around midday so the Senate could send the modestly revamped bill back to the House, and then to Biden this coming week for his signature.

The Senate had been in session since 9 a.m. EST Friday. Its work on the bill was proving to be a test of both lawmakers' physical stamina and Democrats' ability to pass legislation backed by every senator in the party. The chamber is divided 50-50, with Vice President Kamala Harris' tiebreaking vote their only edge, and Republicans are arrayed against the legislation.

Overnight, the Senate was like an experiment in the best techniques for staying awake. Several lawmakers appeared to rest their eyes or doze at their desks, often burying their faces in their hands. At one point, Sen. Brian Schatz, D-Hawaii, at 48 one of the younger senators, trotted into the chamber and did a prolonged stretch.

The huge package — its total spending is nearly one-tenth the size of the entire U.S. economy — is Biden's biggest early priority. It stands as his formula for addressing the deadly virus and a limping economy, twin crises that have afflicted the country for a year.

The bill carries direct payments of up to $1,400 for most Americans, extended emergency unemployment benefits, and lots of spending for COVID-19 vaccines and testing, states and cities, schools and ailing industries, along with tax breaks to help lower-earning people, families with children and consumers buying health insurance.

But the measure was delayed repeatedly as Democrats struck deals and made eleventh-hour changes aimed at balancing demands by their competing moderate and progressive factions.

The lengthy standoffs underscored the headaches confronting party leaders over the next two years — and tensions within the party — as they try moving their agenda through the Congress with their slender majorities.

The measure follows five earlier ones totaling about $4 trillion that Congress has enacted since last spring and comes amid signs of a potential turnaround. Vaccine supplies are growing, deaths and caseloads have eased but remain frighteningly high, and hiring was surprisingly strong last month, though the economy remains 10 million jobs smaller than its pre-pandemic levels.

“Without a rescue plan, these gains are going to slow,” Biden said Friday. “We can’t afford one step forward and two steps backwards. We need to beat the virus, provide essential relief, and build an inclusive recovery.”

But Republicans oppose the bill as a wasteful gift to Democrats' liberal allies that ignores indications of improvement.

“Democrats inherited a tide that was already turning," said Senate Minority Leader Mitch McConnell, R-Ky.

Work on the bill ground to a halt Friday after a deal among Democrats on extending emergency jobless benefits seemed to collapse. But nearly 12 hours later, top Democrats and West Virginia Sen. Joe Manchin, perhaps the chamber's most conservative Democrat, said they had a deal and the Senate approved it on a party-line 50-49 vote.

Under their compromise, $300 weekly emergency unemployment checks — on top of regular state benefits — would be renewed, with a final payment made Oct. 6. There would also be tax breaks on some of those payments, helping people the pandemic abruptly tossed out of jobs and risked tax penalties on the benefits.

The House's COVID-19 relief bill, largely similar to the Senate measure, provided $400 weekly benefits through August. The current $300 per week payments expire March 14, and Democrats want to have the bill on Biden's desk by then to avert a lapse.

Manchin and Republicans have asserted that higher jobless benefits discourage people from returning to work, a rationale most Democrats and many economists reject.

Manchin is a kingmaker in the 50-50 Senate, but Democrats cannot tilt too far center to win his vote without endangering progressive support in the House, where they have a mere 10-vote edge.

That agreement wasn't the only move that helped cement support from party moderates.

The Senate voted on Friday to eject a House-approved boost in the federal minimum wage to $15 an hour by 2025, a major defeat for progressives. Eight Democrats opposed the increase, suggesting that Sen. Bernie Sanders, I-Vt., and other progressives vowing to continue the effort in coming months will face a difficult fight.

In one of many late deals, party leaders restricted eligibility for the $1,400 stimulus checks that will go to most Americans. That amount would be gradually reduced until, under the Senate bill, it reaches zero for people earning $80,000 and couples making $160,000. Those amounts were higher in the House version.

Most of the overnight and morning amendments were by Republicans and were defeated. Many amendments were either attempts to force Democrats to cast politically awkward votes or for Republicans to demonstrate their zeal for issues that appeal to GOP voters.

These included defeated efforts to bar the bill's education funds from going to schools closed for the pandemic that don't reopen their doors, or from schools that let transgender students born male to participate in female sports. One amendment would have blocked aid to so-called sanctuary cities, where local authorities balk at helping federal officials round up immigrants who are in the U.S. illegally.

Friday's gridlock over unemployment benefits gridlock wasn't the first delay on the relief package. On Thursday Sen. Ron Johnson, R-Wis., forced the chamber's clerks to read aloud the entire 628-page relief bill, an exhausting task that took staffers 10 hours and 44 minutes and ended shortly after 2 a.m. EST Friday.

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Associated Press writers Lisa Mascaro and Kevin Freking contributed to this report.