WASHINGTON (AP) — President Joe Biden overcame skepticism, deep political polarization and legislative gamesmanship to win bipartisan approval in the Senate this week of his $1 trillion infrastructure bill.

But as the bill moves to consideration in the House alongside a $3.5 trillion budget that achieves the rest of Biden's agenda, the president is facing an even more complicated task. He must keep a diverse, sometimes fractious Democratic Party in line behind the fragile compromises that underpin both measures.

If Biden and Democratic leaders in Congress hope to succeed with what they've called a two-track legislative strategy, the months ahead will almost certainly be dominated by a tedious balancing act. With exceedingly slim majorities in Congress, Biden can't afford many defections in a party whose members include moderates and progressives.

“Is it going to be easy?” Senate Majority Leader Chuck Schumer said Wednesday. “Absolutely not. But if past is prologue, we got a chance — a decent chance.”

The intra-party jockeying began even as the Senate was putting the finishing touches on its overnight voting marathon that didn’t end until nearly dawn Wednesday. In a letter to leadership, Sen. Joe Manchin of West Virginia, one of two high-profile moderate senators, expressed misgivings about the size of the $3.5 trillion package.

At the same time, progressives in the House, fresh off forcing the administration's hand on reviving a moratorium on evictions, have made clear they see a moment to wield power.

With no votes to spare in the evenly split 50-50 Senate and a slim margin in the House, any single senator or a few representatives could deny Biden the majority he needs for passage. Knowing that they must appease all in their party, Biden and the Democratic congressional leadership have pushed to simultaneously pursue the infrastructure and budget bills.

But Kyrsten Sinema, the enigmatic Arizona senator who stands as one of the moderates in the caucus, already announced her position, declaring she cannot vote for a $3.5 trillion package. And on Wednesday, Manchin made it clear that he, too, believes the current price tag is too much.

“It is simply irresponsible to continue spending at levels more suited to respond to a Great Depression or Great Recession — not an economy that is on the verge of overheating,” Manchin said in a statement. He urged colleagues “to seriously consider this reality as this budget process unfolds.”

Biden on Wednesday seemed to take aim at the moderates’ concerns that his plan would pump too much money into the economy, declaring that his agenda was “a long-term investment” and ”fiscally responsible.”

The president portrayed the package not as economic stimulus, but as a more substantial reworking of the support provided for child care, elder care and other aspects of American life.

“If your primary concern right now is the cost of living, you should support this plan, not oppose it,” the president said.

In the House, a similar dynamic is at play, as nine centrist Democratic lawmakers sent Speaker Nancy Pelosi a letter this week warning against big spending in the budget bill. House Democrats are expected to take up the budget resolution for a vote later this month, but the holdouts suggested they would resist a package of that size amid the backdrop of potentially rising inflation and debt, and the new expenditures that could be needed to tackle the coronavirus pandemic.

Some moderates feared that a vote in favor of the bigger bill could cost them their seats next fall; one moderate Democrat, veteran Rep. Ron Kind of Wisconsin, announced Tuesday that he was retiring.

But House progressives argued the opposite approach, saying they could not consent to passing the bipartisan bill without the bigger package.

Rep. Pramilia Jayapal, the chairwoman of the Congressional Progressive Caucus, said voters gave Democrats control of Congress and the White House to “not only to improve roads and bridges, but to improve their daily lives, too. We can do that by using this governing moment to ensure that President Biden’s complete agenda is realized.”

On a call with the House Democratic caucus Wednesday, Pelosi reiterated her position that both the bipartisan bill and the broader package will move in tandem, according to a person granted anonymity to discuss the private call.

“The President has said he’s all for the bipartisan approach: Bravo!” Pelosi told the lawmakers, the person said. While that’s progress, she said, “It ain’t the whole vision.”

Pelosi told the lawmakers she was not “freelancing” in her approach but relying on what she called the “consensus” position of the caucus. The Senate began its recess Wednesday but the House will return in less than two weeks.

From Biden’s blueprint, the package will essentially rewire the social safety net and expand the role of government across industries and livelihoods, on par with Franklin D. Roosevelt’s New Deal or Lyndon B. Johnson’s Great Society. White House aides are encouraged that, so far, both the liberals and moderates have engaged in mere saber rattling with no red lines drawn.

Much as they did during the Senate infrastructure negotiations, Biden and senior staffers will relentlessly work the phones to assuage wary members while understanding that both sides need to publicly defend their positions. And the president is expected to travel in support of the bills later this month.

“I think we will get enough Democrats to vote for it,” Biden said Tuesday. “For the Republicans who supported this bill, you showed a lot of courage. To the Democrats who supported this bill, we can be proud.”

Schumer convened a private meeting this week of the Senate committee chairmen who will be drafting what is certain to be an enormous bill, giving them a Sept. 15 deadline to produce the legislation. House chairs have been similarly at work.

The majority leader acknowledged the tough road ahead, noting the diversity of views among senators — from Vermont's Bernie Sanders, who initially proposed a more sweeping, nearly $6 trillion plan, to Manchin and those in the center. But he said Democrats are united in their desire to get it done.

“We have a diverse caucus, from Bernie Sanders, we have Joe Manchin, and everybody in between,” Schumer said. “There are some in my caucus who might believe it’s too much. There are some in my caucus we believe it's too little. We are going to all come together to get something done.”

An array of progressive and pro-White House groups will aim to keep Democrats in line by spending nearly $100 million to promote Biden’s agenda while lawmakers are on recess. An outside coalition of progressive organizations launched a war room and is planning to host over 1,000 events and actions to bombard the home districts of members of Congress with ads — both televised and digital — to keep the pressure on to follow through on their votes as well as to underscore much of the agenda’s popularity with the public.