Just hours after Georgia voters elected two Democrats, flipping the Senate majority, on Jan. 5, Sen. Charles E. Schumer reveled in the victory and said his caucus — handed power for the first time in six years — was “committed to delivering the bold change and help that Americans need and demand.”

In the months since, Schumer has repeatedly promised “big and bold” solutions to the problems ailing America. He now may be on the cusp of delivering them amid his most perilous test of leadership yet, with a bipartisan infrastructure deal moving closer to fruition, a multi-trillion-dollar economic and social policy plan waiting in the wings, and the fate of President Biden’s governing agenda hanging in the balance.

The fresh progress has come as memories of the legislative bravura that pushed a sweeping $2 trillion pandemic relief package through a 50-50 Senate back in March have faded and Democrats have been dealt setbacks on key issues, such as voting rights and police reform.

They now confront the much more intricate task of advancing two landmark bills in tandem — one favored by centrist Democrats that is being negotiated with Republicans, the other intended to be passed solely with Democrats.

A 67-to-32 vote Wednesday night advanced the bipartisan infrastructure deal that has been brewing for months, and Schumer on Thursday declared the “two-track” strategy he orchestrated with the help of White House officials to be “on track.”

“Some pundits have called that a tall order. I understand that. But because of the vote last night, the Senate is now moving forward,” he said. “It took some prodding and a few deadlines, but it all has worked out for the better.”

If Schumer can pull it off in the coming weeks, it would rank among the most significant feats of lawmaking in recent American history. Still, pitfalls are ever present, and even senators who credit Schumer with shepherding the process this far are careful not to declare victory prematurely.

“This is a long process — you have to have patience — but it is a good first step,” said Sen. Catherine Cortez Masto (D-Nev.). “We have discussions, sometimes not easy discussions. But he’s allowed us to talk with one another, engage with one another, but at the end of the day, keep the caucus united to really focus on what it is we are trying to achieve.”

Liberals such as Budget Committee Chairman Bernie Sanders (I-Vt.) are eager to get moving with the large Democrats-only bill, which would provide massive spending increases for education, child care and climate programs. And some of the party’s most senior members are chafing because the committees they lead have been sidelined by the group that negotiated the package to upgrade the nation’s roads, bridges, pipes, ports and Internet connections.

Meanwhile, Democratic centrists are fully invested in the bipartisan infrastructure talks — not to mention Biden — and some are suggesting that the larger bill, which will likely need to be passed on party lines under special budget “reconciliation” procedures, needs to be reined in.

That dynamic was underscored Wednesday when Sen. Kyrsten Sinema (D-Ariz.), a lead architect of the bipartisan deal, issued a statement saying she would oppose a reconciliation bill to spend $3.5 trillion — a figure agreed to by Democratic members of the Senate Budget Committee who are sketching out the framework for that legislation.

The crosscurrents would make progress difficult with a substantial majority, let alone with a 50-50 split, and the Republicans supporting the bipartisan deal are essentially betting that Schumer will not be able in the end to pull off the two-step.

“I wish I felt sympathy for him,” Minority Whip John Thune (S.D.), the No. 2 GOP leader in the Senate, said with a chuckle. “But I just think it’s part of the job.”

But several Democrats said this week that if anyone has the skills to pull off the audacious feat, it’s Schumer — who spent 18 years in the House before winning election to the Senate in 1998, earning a reputation as an insatiable political animal but also a skilled dealmaker who has brokered agreements on issues from immigration to crime-fighting to financial regulation.

He played a role in recruiting and electing many of his fellow Democrats as a leader of the party campaign committee, and several of those now-colleagues said he proved his mettle keeping Democrats united during the Trump administration.

Inside a private caucus lunch Wednesday, Schumer announced he had secured the votes for both the infrastructure bill and a budget resolution — a key prerequisite to passing the larger Democrats-only bill.

Sen. Jon Tester (D-Mont.) spoke up at that point, according to two Democrats familiar with the exchange, and said it couldn’t have happened without Schumer’s efforts — prompting a round of applause for the leader.

The dilemma Schumer faces is rooted in arithmetic: As leader of a 50-50 majority dependent on Vice President Harris’s tiebreaking vote, Schumer cannot afford to have any naysayers inside his ranks on matters of raw partisan muscle — such as advancing the social safety net legislation with only Democratic votes.

Sen. Christopher A. Coons (D-Del.) and others said that Schumer understands the necessity of the two-track approach from both a political and policy perspective. On the politics, a host of Democrats — starting with Biden — are heavily invested in delivering a bipartisan victory on a major national issue. And on the policy side, there are portions of an infrastructure bill that simply can’t be passed under reconciliation procedures and must be negotiated with Republicans.

“They are both vehicles for making real the core elements” of the Biden agenda, Coons said. “But they rely on different coalitions to pass and they are going to follow different paths to enactment.”

The stakes for Schumer and his party are immense: The economic bills could be Democrats’ last chance to pass major legislation before the 2022 midterm elections. Other major bills, such as those dealing with voting rights and policing, have become bogged down in partisan infighting. And while some Democrats have softened on eliminating the filibuster, Sen. Joe Manchin III (D-W.Va.) and Sinema remain steadfast in refusing to touch the rule that empowers the minority party by requiring 60 votes to advance most legislation in the Senate.

Schumer on Thursday called the advancement of the bipartisan deal proof that Biden and Democrats were delivering on their campaign promises.

“Such a difference between the bumbling, nasty, divisive last two years of the Trump administration and a new Democratic majority in the House and Senate and a Democratic president,” he said.

With the infrastructure deal crucial to unlocking the broader Democratic wish list, Schumer has played a quiet but persistent role in the talks, speaking multiple times a day with Ron Klain, the White House chief of staff.

Sen. Mark R. Warner (D-Va.), a key player in the negotiations, called Schumer “relentless but patient” and described “virtually daily” conversations about how to clinch a deal.

“He’s earned his pay,” he said.

Much of Schumer’s internal politicking has been focused on the centrist wing of the caucus, drawing on relationships that go back a decade or more.

Unlike his predecessor as Democratic leader, Harry M. Reid of Nevada, Schumer enjoys a close, friendly relationship with Manchin, for instance. He was a frequent enough visitor to Manchin’s houseboat that the West Virginian told Time magazine in 2014 that “Schumer thinks it’s his boat.”

He has given Manchin a wide berth to represent his deep-red state and has viewed attempts to openly pressure him as counterproductive, confidants say. Manchin, in turn, has delivered key votes over the past seven months for Biden’s coronavirus rescue plan and for most — though not all — of his most controversial nominees.

Schumer has also kept Manchin in the fold on another issue — voting rights — that has bedeviled Democrats. Manchin joined several senators involved in the issue inside Schumer’s office Wednesday. They emerged promising a revised bill, expected to follow a framework sketched out by Manchin, that is meant to keep the issue front and center even as the Senate turns to the economic bills.

Schumer, who is up for reelection in 2022, is facing intense liberal pressure as well, with members pushing for the inclusion of myriad priorities in the catchall reconciliation bill, including immigration provisions and aggressive new climate standards. He has responded by embracing some of the left’s key demands, such as the blanket forgiveness of billions of dollars in federally held student debt, while simultaneously shepherding the bipartisan deal.

The threat and pressure Schumer faces from liberals was evident Wednesday night when Rep. Alexandria Ocasio-Cortez (D-N.Y.) — a possible, if unlikely, primary challenger — reacted angrily to Sinema’s statement she didn’t support $3.5 trillion in additional funding for an expansion of the social safety net.

“Good luck tanking your own party’s investment on child care, climate action, and infrastructure while presuming you’ll survive a 3 vote House margin — especially after choosing to exclude members of color from negotiations and calling that a ‘bipartisan accomplishment,’ ” she wrote on Twitter.

Senators and aides familiar with the internal deliberations inside the Democratic caucus said Schumer has been mindful of balancing the need to let the bipartisan talks play out at their own pace with the need to avoid endless delays.

With time lapsing and talks stalling earlier this month, Schumer moved to nudge them along by announcing a surprise vote to bring the issue to the Senate floor, even without a deal in place. Republicans immediately erupted in protest, with some insisting the move was proof Democrats wanted to blow up the deal and move forward with their larger bill.

But Schumer calculated that the talks needed a push, and before moving forward with the vote, he called the five main Democratic infrastructure negotiators to his office to get their okay. The initial vote two days later failed, but the talks intensified, setting the stage for Wednesday’s breakthrough.

“We were always trying to go fast,” said one Republican involved, who spoke on the condition of anonymity to speak candidly about the negotiations. “But . . . it encouraged everyone to be more focused, including the White House.”

Schumer has signaled he plans to keep the pressure on, and he has one of a congressional leader’s most powerful weapons in his back pocket: the threat of losing a scheduled recess — time that lawmakers cherish for campaigning, overseas official travel and good old R&R.

“We’re going to get this done,” Schumer told reporters Tuesday. “Through the August recess, if we have to stay. Period.”