The Alliance of Automobile Manufacturers favors incremental increases each year, saying its members want to increase gas mileage to meet consumers' expectations. The group represents automakers that build 70 percent of all cars and light trucks sold in the U.S., including BMW Group, Fiat Chrysler Automobiles, Ford, GM, Mazda, Mercedes-Benz, Toyota and Volkswagen.
"Just like towing capability or power or headroom, legroom, you name it, this is another attribute where manufacturers compete," Christopher Nevers, vice president of energy and environment for the alliance, told Automotive News. "So it's only natural that a manufacturer is seeking to do more there."
Nevers added, "I really think some of it is the social responsibility aspect."
Although BMW, Ford, American Honda and Volkswagen all signed the California agreement, Trump singled out Ford from that group in a series of tweets last week. He also dragged GM into the fray, even though it wasn't part of the deal.
Trump called auto executives "foolish" for being "willing to spend more money on a car that is not as safe or good, and cost $3,000 more to consumers."
His tweets repeated the administration's belief that lighter, more fuel-efficient cars are less safe and more expensive. Trump said the companies were going along with California to be "politically correct" and that the state would "squeeze them to a point of business ruin."
Ford disagreed. It didn't respond directly to all of Trump's claims but said it has consistently supported a 50-state solution for fuel economy standards and that the California arrangement would provide "regulatory stability while reducing CO2 more than complying with two different standards."
The company said it "will continue to produce ever cleaner, smarter and safer vehicles."
GM, meanwhile, said it's focused on "working with all parties" on a deal that would include a 50-state solution and a national electric vehicle program. "The pathway includes continuously improving fuel economy and our commitment to an all-electric future," GM said in a statement.
A Honda spokeswoman said the agreement "will provide regulatory stability to the signatory automakers and will secure more CO2 reductions than if two separate standards were implemented."
Honda said in July that the proposed regulatory framework with California results in a simple, national greenhouse gas program and "avoids the patchwork of overlapping federal and state regulations that exists now."
Cox Automotive said automakers recognize that California, the nation's largest vehicle market, and the states that follow its lead are key to sales. California accounts for about 13 percent of all U.S. new-vehicle sales, according to Cox.
That state and those that have adopted its emissions standards represent about 38 percent of the market, "numbers automakers can't ignore," Cox Automotive said in a statement.
The Detroit automakers' relationships with Trump have been on a seesaw for years. Trump is often quick to praise the companies for job-creating assembly plant investments that strengthen the U.S. work force. That goodwill can turn in an instant when news emerges of plant shutdowns and layoffs. Trump also has criticized the globalization of the industry, which he says has cost American jobs.
The alliance's Nevers said he wouldn't rule out the possibility of a compromise between the automakers and government just yet, saying "hope springs eternal."
"What you hear out there with the California and four-automaker agreement is somewhere between the preferred pathway that was proposed by the Trump administration and that which the Obama administration had initially finalized," Nevers said.
"I think there's still a chance that we could all come together and settle somewhere that makes everybody happy."