WASHINGTON >> Brushing past moderates, House Democratic leaders tried to muscle President Joe Biden’s multitrillion-dollar budget blueprint over a key hurdle tonight, hoping to shelve for now an intraparty showdown that risks upending their domestic infrastructure agenda.

Tensions rose as lawmakers returned for the evening session and a band of moderate lawmakers threatened to withhold their votes for the $3.5 trillion plan. They were demanding the House first approve a $1 trillion package of road, power grid, broadband and other infrastructure projects that’s already passed the Senate.

But as the evening dragged on the chamber came to a standstill and plans were thrown into flux as leaders and lawmakers huddled privately at the Capitol trying to broker an agreement.

House Speaker Nancy Pelosi implored Democrats during a private caucus not to bog down and miss this chance to deliver on the promises Biden and the party have made to Americans.

“Right now, we have an opportunity to pass something so substantial for our country, so transformative we haven’t seen anything like it,” Pelosi said, according to a person who requested anonymity to disclose the private comments.

Pelosi told them it was “unfortunate” they were discussing the process when they should be debating the policy. “We cannot squander this majority and this Democratic White House by not passing what we need to do,” she said.

With Republicans fully opposed to the president’s big plans, the Democratic leaders were trying to engineer a way out of a potentially devastating standoff between the party’s moderate and progressive wings that risks Biden’s agenda.

Pelosi’s leadership sought to sidestep the issue by persuading lawmakers to vote to simply start the process and save the policy fight for the months ahead, when they will be crafting and debating details within the full $3.5 trillion budget proposal.

One by one, powerful committee chairmen urged their colleagues to move forward.

“There’s a long way to go on legislative issues that are going to play out over the next month. But for the moment the argument here is about: Shall the House proceed,” said Rep. Richard Neal, D-Mass., the chairman of the Ways and Means Committee.

It was unclear if the moderates were fully on board and as soon as one meeting broke, another private session was convened with them for further discussion. What had been a night of scheduled votes came to an unexpected standstill.

Confronting their party’s most powerful leaders, nine moderate Democrats signed onto a letter late last week raising their objections to pushing ahead with Biden’s broader infrastructure proposal without first considering the smaller public works plan that has already passed the Senate. Other moderates raised similar concerns in recent days.

“I’m bewildered by my party’s misguided strategy to make passage of the popular, already-written, bipartisan infrastructure bill contingent upon passage of the contentious, yet-to-be-written, partisan reconciliation bill,” wrote Rep. Stephanie Murphy, D-Fla., a leader of the centrist Blue Dog caucus, in the Orlando Sentinel. “It’s bad policy and, yes, bad politics.”

In the narrowly divided House, every vote matters and a few dissenters could conceivably end the Democratic majority’s hopes for passing any proposal.

With most of Biden’s domestic agenda at stake, it’s unimaginable that Pelosi, D-Calif., would allow an embarrassing defeat. That’s especially true because the package is stocked with priorities like child care, paid family leave and a Medicare expansion that are hard-fought party goals, and at a time with the president already under criticism over his handling of the U.S. withdrawal from Afghanistan.

The $3.5 trillion budget resolution will set the stage this fall for setting further legislation directing money to be spent on the social safety net, environment and other programs over the next decade.

That huge measure is at the heart of Biden’s vision for helping families and combating climate change and is progressives’ top priority, all of it largely financed with tax increases on the rich and big business.

Progressives signaled early on they wanted the Biden budget priorities first before they agree to the smaller package, worried it would be an insufficient down-payment on his goals.

But the moderates want the opposite, insisting Congress quickly send the smaller, bipartisan infrastructure measure to Biden so he can sign it before the political winds shift. That would nail down a victory they could point to in their reelection campaigns next year.

“The House can’t afford to wait months or do anything to risk passing” the infrastructure bill, Rep. Josh Gottheimer, D-N.J., said late last week. He’s a leader of the nine moderate mavericks who each released statements reaffirming a desire that the infrastructure vote come first.

So far, the White House has backed Pelosi as she led her party in a tightly scripted strategy that aims to keep moderate and progressive lawmakers on board.

White House press secretary Jen Psaki on Monday underscored Biden’s support for Pelosi’s plans. Psaki deemed it a “healthy debate” within the party and said that it was “a high-class problem to have” as Democrats debate the particulars of the legislation.

Republicans said the $3.5 trillion effort that Democrats are seeking to advance fails to address “the crisis that American families are facing” and would lead to higher inflation and deficits.

“The inflation crisis, the border crisis, the energy crisis, the Afghanistan crisis — this budget only makes it worse,” said Rep. Jason Smith of Missouri, top Republican on the House Budget Committee.