Led by California, 13 states are engaged in what promises to be a protracted conflict with the Trump administration over stricter emission and fuel efficiency standards for cars and trucks.

Following up on his campaign promises, President Donald Trump pledged last month at a Detroit automotive testing center to ease emission rules he claimed were stifling economic growth.

He has support from automakers, who climbed aboard the fuel efficiency bandwagon during President Barack Obama’s tenure but now say it would be too expensive to meet the timetable of reaching 54.5 miles per gallon for new cars and trucks by 2025.

On March 24, nine days after Trump’s speech, the California Air Resources Board picked up the gauntlet by voting unanimously to push ahead with the stricter emissions standards. This board has been in the national vanguard for emissions control since its creation in 1967 under a law signed by Gov. Ronald Reagan.

In 2009, the Environmental Protection Agency granted California a waiver under the Clean Air Act to set its own standards for greenhouse gas emissions from motor vehicles.

California standards have influenced automakers because the Golden State is the nation’s largest auto market, and even more because they have been adopted by a dozen other states, including Massachusetts, New Jersey, New York and Pennsylvania. Together, these 13 states have a population of more than 130 million and comprise a third of the nation’s vehicle market.

If the state Air Resources Board had its way, fuel efficiency standards would become tougher.

“All of the evidence — call it science, call it economics — shows that if anything, these standards should be even more aggressive,” said board member Daniel Sperling, a transportation expert at UC Davis.

Several like-minded states have risen to the defense of the California board.

“We’ve come a long way together,” Steven Flint, director of the air resources division of the New York Department of Environmental Conservation, told The New York Times. “We’re with you and believe in what you’re doing.”

Meeting the 54.5 mile per gallon standard by 2025 would require automakers to nearly double present fuel efficiency standards and increase reliance on electric cars, which use no gasoline, and plug-in hybrid vehicles, that can use both electricity and gas.

Electric cars and hybrids (EVs) are presently a tiny fraction of the motor vehicles on U.S. highways — about 600,000 vehicles out of a total of 264 million — but sales of EVs were solid in 2016 and have soared since Trump was elected. Several U.S. cities recently placed an order for 114,000 electric vehicles.

The fight over EVs has more fluid battle lines than the related conflict between the Trump administration and the California-led coalition on overall fuel efficiency. Sales of EVs have benefited considerably from state tax credits or other subsidies and at least 10 states, including some relatively liberal ones such as Illinois, are proposing to eliminate them.

Even so, economists expect the EV market to grow as technology improves and costs drop.

“In the next five to 10 years, every car on sale will offer a hybrid, plug-in hybrid or full EV variant, and the adoption rate of these technologies will increase dramatically,” predicted Nicholas Roche, a mechanical design engineer at Tesla, a leading manufacturer of EVs.

Conventional vehicles have also become more efficient. Automotive analyst Kyle Stock, writing for Bloomberg, credited aluminum alloys that allow lighter body panels, cylinders and turbos that shut down when they aren’t needed, and continuously variable transmissions.

“What’s interesting is that many of the engineering improvements are driven by performance as much as environmental concerns,” Stock wrote. “Mercedes engineers didn’t put two turbos in their latest race car because they were worried about asthma rates; they did it to make a quicker machine.

Ford didn’t sheath its F-150 lightweight pickup trucks in lightweight aluminum to help Texas ranchers save $3 at the pump. They did it so the rig would weigh less and tow more.”

Despite such improvements, industry groups say that the technological challenges of reaching the 2025 fuel standards are steep. Mitch Bainwol, president and CEO of the Alliance of Automobile Manufacturers, estimates it will cost the industry $200 billion to produce vehicles with average fuel efficiency of 54.5 miles a gallon.

Environmental groups contend this estimate is exaggerated, while various auto experts have warned that it could be risky for the U.S. auto industry to become a global laggard on efficient cars as other countries move forward.

Standards for fuel efficiency and greenhouse gas emissions were first set jointly by the EPA and the National Highway Traffic Safety Administration, covering the period from 2010 to 2016. In 2012, these federal agencies coordinated with the California Air Resources Board to extend the goals through 2025.

The intent of these three agencies was to develop a single national standard rather than a separate one for California and states that adopted its strict emission rules. Because 2025 was so far away, the agencies agreed to have a “midterm review” in 2018.

Trump promised during the 2016 election campaign to loosen environmental regulations. After he was elected, the Obama administration moved up the midterm review. Citing technical studies, Obama’s EPA decided a week before Trump took office that the original fuel efficiency standards for 2025 should not be changed.

This decision, designed to head off any changes that the Trump administration might promulgate, triggered a wave of protests from U.S. automakers.

In his Detroit speech, Trump assured the auto industry that he would reinstate the 2018 midterm review of the fuel efficiency standards.

EPA administrator Scott Pruitt, a former Oklahoma attorney general known for his friendliness to the oil industry, said the standards “are costly for automakers and the American people.”

Trump’s action and the subsequent affirmation of the standards by the California Air Resources Board were opening shots in what promises to be a long domestic war over environmental issues.

There aren’t yet many casualties in this conflict: It would take hearings and possibly years of legal battles before the fuel efficiency standards could be changed.

The EPA could also try to strip California of the waiver that permits it to set its own standards. Pruitt has so far declined to say if he will take this action, which also would provoke a legal struggle.

More is at stake than fuel efficiency, important as this is.

Although Trump has backed away from campaign claims that climate change is a “hoax,” his proposed budget would eliminate climate change research and prevention, and slash the EPA budget by 31 percent, more than any other agency.

He is also moving toward ordering the EPA to dismantle Obama-era regulations on pollution from coal-fired power plants.

Trump’s systematic challenge to the Obama environmental legacy puts the federal government on a collision course with California and other states that want stricter, not weaker, environmental guidelines.

Gov. Jerry Brown and the Legislature, in which Democrats hold a super-majority, have reaffirmed their determination to continue toward a goal that would reduce the state’s carbon emissions 40 percent below 1990 levels by 2030. Brown has also joined with fellow a Democrat, New York Gov. Andrew Cuomo, in challenging Trump’s premises.

“Dismantling the Clean Power Plan and other critical climate programs is profoundly misguided and shockingly ignores basic science,” Brown and Cuomo said in a joint statement. ”With this move, the administration will endanger public health, our environment and our economic prosperity.”

New York has goals for fighting global warming nearly as ambitious as California’s and equivalent targets for reducing greenhouse gas emissions. The two states are pushing to generate half their electricity from renewable sources by 2030 and have indicated their readiness to seek global allies toward this end.

“With or without Washington, we will work with our partners throughout the world to aggressively fight climate change and protect our future,” Brown and Cuomo said.

It’s a battle of competing priorities between Trump and a handful of Democratic coastal states that wield considerable influence. Neither side shows any sign of backing down.

Lou Cannon, a Summerland resident, is a longtime national political writer and acclaimed presidential biographer. His most recent book — co-authored with his son, Carl — is Reagan’s Disciple: George W. Bush’s Troubled Quest for a Presidential Legacy. Cannon also is an editorial adviser to State Net Capitol Journal, which published this column originally. Click here to read previous columns. The opinions expressed are his own.

Lou Cannon, a Summerland resident, is a longtime national political writer and acclaimed presidential biographer. His most recent book — co-authored with his son, Carl — is Reagan’s Disciple: George W. Bush’s Troubled Quest for a Presidential Legacy. Cannon also is an editorial adviser to State Net Capitol Journal, which published this column originally. Click here to read previous columns. The opinions expressed are his own.