WASHINGTON — Senator Chuck Schumer was huddled in his Capitol office on Thursday evening awaiting a climactic meeting with Kyrsten Sinema, a critical holdout on his painstakingly negotiated climate change, tax and health care deal, when the loud booms and flashes of a powerful thunderstorm shook Washington, setting the lights flickering.
Mr. Schumer and his aides, so close to a signature legislative achievement to top off a surprise string of victories, glanced anxiously at one another and wondered if it was a bad omen. A 50-50 Senate, a pandemic that kept Democrats constantly guessing about who would be available to vote and the sheer difficulty of managing the nearly unmanageable chamber had left them superstitious.
“I’ve been a worrier all my life, but a happy worrier,” said Mr. Schumer, Democrat of New York and the majority leader.
He needn’t have fretted. After a half-hour meeting, Mr. Schumer shook hands with Ms. Sinema, Democrat of Arizona, who agreed to lend her support to the legislation in exchange for a few revisions and some home-state drought relief. After a grueling overnight session, the Senate approved the sweeping measure on Sunday, with Vice President Kamala Harris casting the tiebreaking vote. The House was expected to follow suit later this week.
It was a head-snapping change in fortune. Just a few weeks earlier, Mr. Schumer, the Democratic agenda and the party’s chances of retaining its bare Senate majority all seemed in sorry shape as last-gasp negotiations over the broad legislation appeared to collapse for good under the weight of resistance from Senator Joe Manchin III, Democrat of West Virginia.
Instead, Democrats not only landed their biggest prize — the party-line climate-and-tax legislation — but also capped off an extraordinarily productive run for a Congress better known for its paralysis. It included passage of the first bipartisan gun safety legislation in a generation, a huge microchip production and scientific research bill to boost American competitiveness with China, and a major veterans health care measure.
The series of successes was all the more sweet for Democrats because it came with the political benefit of Republicans making themselves look bad by switching their position and temporarily blocking the bill to help sick veterans, in what appeared to be a temper tantrum over the abrupt resurrection of the climate deal.
“We’ve had an extraordinary six weeks,” Mr. Schumer said in an interview, calling the climate, health and tax measure “the most comprehensive piece of legislation affecting the American people in decades.”
It was far from certain he could attain this result. Mr. Schumer, who unlike his predecessors is not known as a master tactician or gifted legislator, has struggled to produce for long stretches, needing every single vote from an ideologically mixed Democratic membership. Even his allies wondered whether he was too driven by a need to be liked or his own personal political considerations in warding off a potential primary challenge from his left to be capable of the kind of ruthlessness that would be needed.
Mr. Schumer said it was stamina, not bare knuckles, that had been the main requirement.
“This is the hardest job I’ve ever had, with a 50-50 Senate, a big agenda and intransigent Republicans,” Mr. Schumer said. He cited a persistence instilled in him by his father, who ran an exterminating company and died last year, as a motivating factor. “Keep at it, keep at it. Look at all the pitfalls we have faced to get this done.”
Understand the Aug. 2 Primary Elections
While the Trump wing of the Republican Party flexed its muscle, voters in deep-red Kansas delivered a loud warning to the G.O.P. on abortion rights.
The swing on Capitol Hill was palpable as Democrats allowed themselves to hope that their legislative victories, coupled with a national abortion fight they felt was jolting the political landscape in their favor, might keep them in control of the Senate. And for once, they thought they had outfoxed Senator Mitch McConnell, the Kentucky Republican and minority leader who has a history of successfully confounding the Democrats.
“The mood is exuberant, expectant and really ecstatic with the progress we’ve made over the past weeks,” said Senator Richard Blumenthal, Democrat of Connecticut.
Mr. Schumer notched the wins without deep involvement from the White House. President Biden — who had campaigned for the presidency citing his deep experience cutting bipartisan deals in the Senate — ceded to him much of the responsibility for nailing down the details. The final negotiations with Mr. Manchin proceeded one on one in near-total secrecy.
Republicans licked their wounds as they watched the Schumer-led Democrats push through legislation the G.O.P. was powerless to stop under special budgetary rules. They weren’t sold on the notion that Democrats had dug themselves out of a political hole with a bill they named the Inflation Reduction Act, given that Mr. Biden’s popularity is still sagging and the cost of consumer goods is up.
“The highest inflation in 40 years, 9.1 percent, families are hurting, they can’t afford a full tank of gas,” said Senator John Barrasso of Wyoming, the No. 3 Senate Republican. “The end of the month just came, and they ran out of money before they ran out of month.”
But Democrats pointed to approval of long-sought authority for Medicare to negotiate lower drug prices as something that would appeal to voters, along with the general sense that Democrats were finally getting things done on Capitol Hill. They relished the prospect of reminding voters that Republicans had voted against the drug-pricing measure, and forced Democrats to drop a proposal that would have capped the monthly cost of insulin at $35 for private insurers.
They also pointed to the climate change provisions as a huge leap forward, though not as extensive as Democrats had initially hoped to achieve before Mr. Manchin forced the party to pare back its goals.
“It’s a historic climate bill, and it wasn’t on the scoreboard one month ago,” said Senator Edward J. Markey, Democrat of Massachusetts and a leader on climate issues. “Senator Schumer, working with Manchin, has been able to pull out the key climate provisions that we need. It is not all that we wanted, but it was what we need to begin this effort to lead the rest of the world.”
Democrats also got some help from Republicans. Not only did the blunder on the veterans bill play into their hands, but Democrats said a threat by Mr. McConnell to block the microchip bill should Democrats proceed with the party-line climate and tax legislation backfired by motivating Mr. Manchin to pursue a compromise.
“Any time you threaten a bill you support because you are not getting your way on something else, you are in a bad spot,” said Senator Chris Van Hollen, Democrat of Maryland. “It just looks bad. It was so crassly political.”
While he was getting hammered from the left, Mr. McConnell was also getting pounded from the right for being too accommodating of Democrats on bills such as the microchip measure and the gun measure. But Mr. McConnell has his eye on the midterms as well, and he knows Republicans need suburban voters who might be turned off by knee-jerk obstructionism.
“Just because you have closely divided government doesn’t mean you do nothing,” Mr. McConnell said on Fox News last week. “Just because there is a Democrat in the White House, I don’t think means Republicans should do nothing that is good for the country in the meantime.”
That approach has bolstered Democrats at a crucial moment, entering the heart of the campaign season.
“There is a clear momentum change,” said Senator Gary Peters, Democrat of Michigan and the head of the party’s Senate campaign arm. “I feel like we are in really good place. Here we are going into August coming into Labor Day, and you look at where the numbers are, and our candidates are all doing really well in a tough environment.”
After the recess, Mr. Schumer and fellow Democrats intend to try to press their success, scheduling politically charged votes on same-sex marriage, oil pricing and other issues they think can showcase their strengths and put Republicans on the spot.
But even as he was about to record a major accomplishment, Mr. Schumer was taking no chances. When the leader of an environmental advocacy group heralded him as a hero after an event outside the Capitol on Thursday, Mr. Schumer cautioned him, “Not yet, not yet.”
Mr. Schumer said the outcome underscored a key difference between him and Mr. McConnell, known more for his blockades and killing legislation than passing bills.
“He brags about the graveyard,” Mr. Schumer said. “I’d like to be proud of the achievements, of getting things done — not not getting things done.”