WASHINGTON — President Trump on Wednesday posted on Twitter an aggressive defense of his unprecedented move to abolish California’s legal authority to set its own standards on climate-warming automobile emissions.
Mr. Trump was in Los Angeles for a fund-raiser when he boasted about the move, which California officials and environmental advocates have assailed as an illegal attack on states’ rights and on a major policy designed to fight climate change.
“The Trump administration is revoking California’s Federal Waiver on emissions in order to produce far less expensive cars for the consumer, while at the same time making the cars substantially SAFER,” Mr. Trump wrote in the first of three posts. He said the change would lead to increased auto production and new “JOBS, JOBS JOBS,” and claimed that the newer cars would be “extremely environmentally friendly,”
California officials said they would sue to block the move as soon as the plan was officially published.
“Our message to those who claim to support states’ rights is, ‘Don’t trample on ours,’” said Xavier Becerra, the attorney general of California, at a Sacramento news conference about an hour after Mr. Trump’s tweets. “We cannot afford to backslide in our battle against climate change.”
Mr. Trump’s supporters welcomed the move.
“The California emissions regulations would impact Americans in other states who have no ability to vote those state legislators out of office,” said Adam Brandon, the president of FreedomWorks, a libertarian offshoot of a group co-founded by the late David H. Koch and his brother Charles Koch, who made their fortune in fossil fuels. “It is regulation without representation at its worst.”
The Trump administration is expected Thursday morning to formally revoke California’s authority to set auto emissions rules that are stricter than federal standards, taking a major step forward in the administration’s wide-ranging attack on efforts to fight climate change. Andrew Wheeler, the head of the Environmental Protection Agency, and Elaine Chao, the transportation secretary, are scheduled to announce the formal abolition of the waiver, a keystone of California environmental policy, at the Washington headquarters of the E.P.A.
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A revocation of the waiver would have national significance. Tailpipe pollution is the United States’ largest source of planet-warming greenhouse gas pollution, and California, with roughly 35 million vehicles, is the nation’s largest auto market. California has historically set stronger pollution standards than the federal government, and many of those standards have ultimately influenced national and even international policy.
Thirteen other states follow California’s tighter tailpipe greenhouse gas standards, together representing roughly a third of the national auto market.
The president’s series of three Twitter posts sought to defend the revocation by citing specific details of the plan. As the political battle over the climate emissions has intensified, Mr. Trump’s interest in the policy details of the issue has deepened, according to a person familiar with the matter.
“If you look at the whole tweet thread, this is remarkably specific,” said Barry Rabe, a professor of public policy at the University of Michigan. “It almost moves into policy-wonk territory. If he’s doing this himself, he’s on his policy game.”
Still, Mr. Rabe and other experts said that Mr. Trump’s assertions, while using the language of emissions policy, veered from the facts on several significant points.
Several analysts, for instance, disputed Mr. Trump’s assertion that weakening emissions standards would improve highway safety.
“The president’s claim that high fuel economy negatively affects safety is baseless,” said Shannon Baker-Branstetter, the co-author of an August Consumer Reports analysis concluding that the Trump administration’s rollback of fuel economy standards would have no statistically significant effect on highway safety.
Legal experts said that if Mr. Trump’s move was ultimately upheld by the Supreme Court, it could permanently block states from regulating greenhouse gas pollution from vehicles — a major setback for efforts to control climate change. If it was struck down by the Supreme Court, it would allow states to set separate tailpipe pollution standards from those set by the federal government.
That outcome could split the United States auto market, with some states adhering to stricter pollution standards than others. For automakers, that would be a nightmare.
The move has been widely expected since the summer of last year, when the Trump administration made public its draft plan to roll back the strict federal fuel economy standards put in place by the Obama administration. That draft Trump rule also included a plan to revoke the state’s legal waiver, which was granted to California under the 1970 Clean Air Act.
The administration’s plans have been further complicated because major automakers have told the White House that they do not want such an aggressive rollback. In July, four automakers formalized their opposition to Mr. Trump’s plans by signing a deal with California to comply with tighter emissions standards if the broader rollback goes through.
Mr. Trump, who was blindsided and angered by that announcement, according to two people familiar with the matter, wanted to press forward with a policy that would punish California.
Meanwhile, the Justice Department has opened an investigation into whether the automakers’ deal with California violates antitrust laws.
Automakers responded cautiously. Dave Schwietert, the interim chief executive and president of the Alliance of Automobile Manufacturers, which represents 12 major auto companies, said in a statement that his members would review the details of the plan when it is released “to get the full picture of how this impacts automakers.”
Mr. Trump’s efforts would likely lead to increased oil consumption, and some critics expressed concern against the backdrop of this week’s surge in oil prices following attacks on Saudi oil facilities. The Consumer Reports study concluded that Mr. Trump’s rollback of fuel standards would increase the nation’s consumption of oil by about 320 billion gallons.
“Saudi Arabia is showing us how dependent we are on foreign oil,” said Gavin Newsom, the governor of California, at a news conference.
The Obama-era tailpipe pollution rules that the administration hopes to weaken would require automakers to build vehicles that achieve an average fuel economy of 54.5 miles per gallon by 2025, cutting about six billion tons of carbon dioxide pollution over the lifetimes of those vehicles. The proposed Trump rule would lower the requirement to about 37 miles per gallon, allowing for most of that pollution to be emitted.
White House officials have been eager to move quickly to revoke California’s authority to set its own standards because they want the opportunity to defend the effort in the Supreme Court before the end of Mr. Trump’s first term. The thinking goes that if a Democrat were to be elected president in 2020, the federal government would be unlikely to defend revocation of the waiver in the high court.
The 1970 Clean Air Act, the landmark federal legislation designed to fight air pollution nationwide, granted California the right to set its own, stricter rules because the state already had clean air legislation in place when the act passed.
Over the decades, California requested and received numerous federal waivers to set tighter state-level standards on the tailpipe pollutants that cause smog and respiratory problems, though the federal government did not always grant them.
The waiver in effect now was written after the 2008 financial crisis, when the nation’s automakers were financially teetering. It was part of a deal struck by President Barack Obama to toughen emissions standards nationwide while aligning California’s rules with federal regulations. It was designed to remain in effect until 2025.
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