It's the first step in setting fuel economy standards for 2021-2026 vehicles, standards much lower than created by the Obama administration.
The Obama rules were meant to ensure progress made during the Democrat's presidency would extend beyond it. Automakers over the last decade have employed lighter materials and tweaked vehicle design to boost fuel efficiency, changes that have improved mileage on even the biggest U.S. gas guzzlers.
The publication of the proposal sets up a race among opponents of the change - an unusual mix of environmentalists, automakers, consumer groups and states - to temper the plan before it is finalized this year.
The proposal would also end a federal waiver to California that allowed the it to enact stricter tailpipe standards, thereby limiting the types of cars that can be sold in the nation's most populous state. Those states argue the Clean Air Act empowers them to keep the Obama-era fuel economy standards in place in their markets. Meantime, California remains fully committed to a rigorous 50-state program with a full range of vehicle choices.
The Trump administration proposal could also invalidate California's mandate that automakers sell a certain number of electric vehicles. Potential litigation could result in uncertainty for manufacturers with respect to vehicle sales in California and other states that adopt California's rules, as permitted by Section 177 of the CAA. "We are ready to do what is necessary to hold this Administration accountable".
The Trump administration contends that, by promoting the manufacture and sale of lighter cars, the Obama standards could lead to about 12,700 more auto fatalities.
The Alliance of Automobile Manufacturers, a main industry group, sought to stave off any dispute between California and the federal government that could split the USA auto market: "We urge California and the federal government to find a common sense solution that sets continued increases in vehicle efficiency standards while also meeting the needs of American drivers".
The tough standards favored by former President Barack Obama "are no longer appropriate and reasonable" beyond 2020, according to the proposal released by the Environmental Protection Agency and National Highway Traffic Safety Administration.
In an editorial in The Wall Street Journal, Transportation Secretary Elaine Chao and acting EPA Administrator Andrew Wheeler added that the Trump administration was working to support consumer interests with its national proposal.
Judge in Manafort trial: Don't use word 'oligarchs'
The other 31 people charged have either pleaded guilty or are Russians seen as unlikely to enter an American courtroom. Rudy Giuliani, a lawyer for Trump, said no one facing trial should expect a pardon, but he did not rule one out.
The transportation sector is the largest emitter of greenhouse gases.
The proposal also took a swipe at California, accusing the state of focusing "disproportionately" on greenhouse gas emissions at the expense of overall air quality. The impact of freezing those targets for six years, as the administration favors, would be enormous.
The administration said the freeze would boost US oil consumption by about 500,000 barrels of oil a day by the 2030s, and argued it would prevent up to 1,000 traffic fatalities per year by reducing the price of new vehicles and so prompting people to buy newer, safer vehicles more quickly.
But private transportation experts say there are so many factors involved that the 1,000 lives saved figure is questionable.
"More realistic standards will promote a healthy economy by bringing newer, safer, cleaner and more fuel-efficient vehicles to United States roads", said Transportation Secretary Elaine Chao. And Simon Mui of the Natural Resources Defense Council says they actually want fuel economy to go up. "They have failed before".
"This is an unprecedented and unlawful action that the California officials say, "...flies in the face of congressional intent and would aggravate the harms to consumers, public health, the economy and the environment caused by the weakening of the federal standards".
At a May meeting in the White House, auto firms appealed to Trump to tap the brakes on the administration's aggressive rollback plan. Previous court decisions have upheld California's GHG program and CAA waiver, suggesting it is not preempted by the EPCA.
Those negotiations have gone nowhere. California attorney general Xavier Becerra announced that he would lead 19 attorneys general in a new lawsuit, saying that "California is about progress and 21st century innovation and technology". Becerra and attorneys general from 16 other states sued in May to stop the EPA from scrapping standards that would have required vehicles by 2025 to achieve 36 miles per gallon (58 kilometers per gallon) in real-world driving, about 10 miles (16 kilometers) over the existing standards.