The Biden administration finalized a rule Monday to cut climate pollutants from new cars and light trucks, which will keep billions of tons of carbon dioxide from entering the atmosphere and change the kinds of vehicles Americans drive.

The new limits on tailpipe emissions for the next four years mark President Biden’s biggest step yet to tackle climate change, but the move comes as critical components of his plan for an all-electric future just suffered a major blow on Capitol Hill. On Sunday, Sen. Joe Manchin III (D-W.Va.) announced he would not support his party’s Build Back Better plan, which would have provided billions in federal support for building charging stations and encouraging consumers to buy electric vehicles.

The administration had hoped that funding in the roughly $2 trillion package Democrats have been trying to pass on a strictly party-line vote in the Senate could accelerate America’s transition away from fossil fuels, and make it less likely that industries would challenge new climate rules in court. But given Manchin’s staunch opposition, Biden may have to rely on his executive authority to advance his environmental agenda.

The new standards on their own cannot ensure that half of new cars sold by the end of the decade in the United States will be electric or plug-in hybrids, as Biden had promised. With the rule in place, regulators say, those cars will make up about a fifth of sales by 2026.

But automakers have repeatedly argued that zero-emissions vehicles, which make up less than 5 percent of sales, will not make major strides without the kinds of generous subsidies and tax breaks included in Democrats’ budget package. The bill, which now faces an uncertain future, would save car buyers up to $12,500 in taxes for going electric.

The standards for model years 2023 to 2026, signed Monday morning by EPA Administrator Michael Regan, require that cars, SUVs and pickup trucks release an average of 161 grams of carbon dioxide per mile by 2026. The new Biden standards are equivalent to an average of roughly 55 miles per gallon by 2026 in laboratory testing. The average figure appearing on window stickers — and advertised EPA mileage — would be 40 mpg.

The agency decided to issue tailpipe emissions tighter than those it proposed in August for 2025 and 2026.

Regan addressed a crowd of environmentalists and industry representatives Monday from a podium sandwiched between some of the latest and flashiest battery-powered vehicles, including the Jeep Grand Cherokee, the Chevrolet Bolt and the Ford Mustang Mach-E.

Pressed on whether the industry could meet the tighter pollution standards without the climate bill’s passage, he said at a news conference held in the EPA’s courtyard that the new rule is “achievable.”

“That’s not to say we’re not going to continue to fight tirelessly for those incentives that are in the Build Back Better proposal,” he said. “But, nevertheless, we believe we’ve proposed a rule that’s doable.”

But Alliance for Automotive Innovation CEO John Bozzella, whose members account for nearly all U.S. car and light truck sales, called on the government to provide more support for both car buyers and automakers for going electric, given that the EPA rule “is even more aggressive than originally proposed.”

“Achieving the goals of this final rule will undoubtedly require enactment of supportive governmental policies,” he said in a statement.

The rule will prevent an estimated 3.1 billion tons of carbon dioxide emissions over the next three decades, the agency estimates, which is equal to shutting down more than 700 coal plants for a year. The Transportation Department is in the midst of writing a companion rule aiming to improve the fuel efficiency of cars built between 2024 and 2026.

“That’s about as aggressive as they could have expected to have gone when you’re not giving the automakers hardly any advance notice,” said Jeff Alson, a former engineer at the EPA’s car lab in Ann Arbor, Mich., who worked on the agency’s previous greenhouse gas standards for cars.

But it doesn’t make up for ground lost under the Trump administration, which eased Obama-era rules that would have achieved nearly the same emission cuts a year earlier.

“Climate change has gotten much worse,” said Dan Becker, who directs the Safe Climate Transportation Campaign at the Center for Biological Diversity. “But these rules only require automakers to cut pollution slightly more than they agreed to cut nine years ago.”

“This is not commensurate with tackling an existential threat,” he added. “This is commensurate with making the auto companies whine a lot less.”

The new EPA rule is largely based on a deal struck between California and several automakers in 2019 to improve mileage standards beyond what the Trump administration set. The state — which accounts for more than a tenth of new car sales in the United States — has the power under the Clean Air Act to set more stringent air pollution limits than federal regulators. More than a dozen other states have adopted California’s tailpipe standards as their own, giving it even greater leverage with auto manufacturers.

Many car companies are rushing to retool factories to make battery-powered cars. Toyota announced this month that it is pouring $70 billion into an effort to go electric, aiming to offer 30 electric vehicle models by 2030. And brands such as Mercedes, Volkswagen and General Motors have announced plans to go all or mostly electric.

The transition, though, faces roadblocks.

In Orion, Mich., outside of Detroit, GM converted an existing factory to build its all-electric Chevrolet Bolt. But the production line was halted this year after repeated reports of fires from the vehicles’ lithium-ion batteries. The company retooled another facility in Michigan to all-electric, where it is building its Hummer EV. GM wants to offer 30 electric vehicle models around the world by 2025.

Workers and labor groups have also expressed concerns about the automation and simplification of production lines. Electric powertrains typically contain fewer parts for assembly by autoworkers, leading to fears that an electric future will mean fewer jobs.

Ray Curry, head of the United Auto Workers, was still optimistic that Congress would approve tax breaks for union-made electric vehicles to soften the blow, despite Manchin’s opposition.

“We still believe those EV tax credits will be available for our union-made products, we really do believe that,” Curry said outside EPA headquarters.

Making matters more difficult for regulators is Americans’ growing appetite for gas-guzzling trucks. The EPA under President Barack Obama underestimated the “pretty significant shift from cars to trucks in the market,” Alson said.

Several Republican lawmakers opposed the stricter standards, over fears of further stoking inflation. “This move will only increase the price of cars, which is already historically high,” tweeted Sen. Shelley Moore Capito (W.Va.), ranking Republican on the Senate Environment and Public Works Committee.

Drivers, meanwhile, remain anxious about a dearth of charging stations for battery-powered cars. In densely populated urban areas where home charging is not as feasible, some buyers say electric vehicles are out of the question. The $7.5 billion in the bipartisan infrastructure law signed by Biden for charging stations is likely not enough to build out the network of 500,000 public stations the president wants. The administration had originally called for twice that much money.

“It’d be great if all the cars were electric vehicles tomorrow, but we know that the infrastructure isn’t ready for that, we know that the battery supply isn’t ready for that, and we know the consumer is not ready for that in terms of cost,” said Karl Brauer, executive analyst at the website iSeeCars.com. “I think it’s prudent on the part of the government to say, ‘We can get there, but we can’t get there overnight.’”

The EPA is already planning to restrict emissions further with a rule for cars of model year 2027 and beyond, a make-or-break moment for the president’s 2030 climate goal.

“I’m glad to see the EPA heeded my call to increase its ambition beyond the original proposal and issued a stronger final rule,” Sen. Edward J. Markey (D-Mass.) said in a statement. “But we must continue to raise the bar even further, particularly for the next cycle of vehicle standards.”