WASHINGTON (AP) — Democrats pushed a $3.5 trillion, 10-year bill strengthening social safety net and climate programs through the House Budget Committee, but one Democrat voted “no,” illustrating the challenges party leaders face in winning the near unanimity they'll need to push the sprawling package through Congress.

The Democratic-dominated panel, meeting virtually Saturday, approved the measure on a near party-line vote, 20-17. Passage marked a necessary but minor checking of a procedural box for Democrats by edging it a step closer to debate by the full House. Under budget rules, the committee wasn’t allowed to significantly amend the 2,465-page measure, the product of 13 other House committees.

More important work has been happening in an opaque procession of mostly unannounced phone calls, meetings and other bargaining sessions among party leaders and rank-and-file lawmakers. President Joe Biden, House Speaker Nancy Pelosi, D-Calif., and Senate Majority Leader Chuck Schumer, D-N.Y., have led a behind-the-scenes hunt for compromises to resolve internal divisions and, they hope, allow approval of the mammoth bill soon.

Pelosi told fellow Democrats Saturday that they “must” pass the social and environment package this week, along with a separate infrastructure bill and a third measure preventing a government shutdown on Friday. Her letter to colleagues underscored the pile of crucial work Congress' Democratic majority faces in coming days and seemed an effort to build urgency to resolve long-standing disputes quickly.

"The next few days will be a time of intensity," she wrote.

Moderate Rep. Scott Peters, D-Calif., joined all 16 Republicans on the Budget committee in opposing the legislation. His objections included one that troubles many Democrats: a reluctance to back a bill with provisions that would later be dropped by the Senate.

Many Democrats don't want to become politically vulnerable by backing language that might be controversial back home, only to see it not become law. That preference for voting only on a social and environment bill that's already a House-Senate compromise could complicate Pelosi's effort for a House vote this week.

Peters was among three Democrats who earlier this month voted against a plan favored by most in his party to lower pharmaceutical costs by letting Medicare negotiate for the prescription drugs it buys.

Party leaders have tried for weeks to resolve differences among Democrats over the package's final price tag, which seems sure to shrink. There are also disputes over which initiatives should be reshaped, among them expanded Medicare, tax breaks for children and health care, a push toward cleaner energy and higher levies on the rich and corporations.

Democrats' wafer-thin majorities in the House and Senate mean compromise is mandatory. Before the measure the Budget panel approved Saturday even reaches the House floor, it is expected to be changed to reflect whatever House-Senate accords have been reached, and additional revisions are likely.

The overall bill embodies the crux of Biden's top domestic goals. Budget panel chairman John Yarmuth, D-Ky., cited “decades of disinvestment” on needs like health care, education, child care and the environment as the rationale for the legislation.

“The futures of millions of Americans and their families are at stake. We can no longer afford the costs of neglect and inaction. The time to act is now," Yarmuth said.

Republicans say the proposal is unneeded, unaffordable amid accumulated federal debt exceeding $28 trillion and reflects Democrats' drive to insert government into people's lives. Its tax boosts will cost jobs and include credits for buying electric vehicles, purchases often made by people with comfortable incomes, they said.

“This bill is a disaster for working-class families,” said Rep. Jason Smith of Missouri, the committee’s top Republican. “It’s a big giveaway to the wealthy, it’s a laundry list of agenda items pulled right out of the Bernie Sanders socialist playbook.”

The unusual weekend session occurred as top Democrats amp up efforts to end increasingly bitter disputes between the party's centrist and progressive wings that threaten to undermine Biden's agenda.

Biden conceded Friday that talks among Democrats were at a “stalemate,” though Pelosi and Schumer have been more positive in an apparent effort to build momentum and soothe differences. A collapse of the measure at his own party's hands would be a wounding preview to the coming election year, in which House and Senate control are at stake.

To nail down moderates' support for an earlier budget blueprint, Pelosi promised to begin House consideration by Monday of another pillar of Biden's domestic plans: a $1 trillion collection of roadway and other infrastructure projects. Pelosi reaffirmed this week that the infrastructure debate would begin Monday.

But many moderates who consider the infrastructure bill their top goal also want to cut the $3.5 trillion social and environment package and trim or reshape some programs. They include Sens. Joe Manchin, D-W.Va., and Kyrsten Sinema, D-Ariz.

In response, progressives — their top priority is the $3.5 trillion measure — are threatening to vote against the infrastructure bill if it comes up for a vote first. Their opposition seems likely to be enough to scuttle it, and Pelosi hasn't definitively said when a vote on final passage of the infrastructure measure will occur.

With each portion of the party threatening to upend the other's most cherished goal — a political disaster in the making for Democrats — top Democrats are using the moment to accelerate talks on the massive social and climate legislation. The party can lose no votes in the Senate and a maximum of three in the House to succeed in the narrowly split Congress.