President Trump announced that he is postponing stringent new fuel-economy standards for automobiles for the model years 2022 to 2025, arguing that the Obama Administration jumped the gun in approving the new targets earlier this year.

The fuel standards will now undergo a previously scheduled “midterm review” by automakers and regulators sometime this year. The review is part of the car industry’s 2012 agreement with regulators to meet tougher fuel-economy standards in order to reduce carbon emissions and combat climate change.

Because fuel-economy standards are already locked in through the 2021 model year, nothing will change for several years. Still, the president’s decision has alarmed environmentalists and consumer groups. It also has reignited the debate over how best to protect the environment while still producing cars that consumers want to buy.

To understand what’s at stake, here’s a look at the key issues involved.

What Happened Today?

President Trump is reversing a decision made by the Obama administration in early January to proceed with the tougher fuel targets for the 2022 to 2025 model years. Trump is siding with the auto industry, which argued that Obama officials adopted the standards before car makers and regulators could fully review the targets.

Today’s decision doesn’t actually roll back the tougher fuel guidelines. It simply puts them on hold until the review can take place later this year.

This “midterm” review was deemed necessary because it wasn’t clear in 2012, when the fuel targets were agreed to, what kind of technology would be available in 2017. The review is also supposed to look at how the technology is working in real-world cars and how market conditions, such as the price of gas, are affecting sales.

There was some speculation that the Trump administration would also address California’s even tougher emission standards for cars, which the auto industry complains forces them to comply with two different fuel-economy targets. That issue was not mentioned today but could come up later—especially if California and the federal government differ in their assessments of climate change and the need to aggressively curtail carbon dioxide emissions.

Why Did Obama’s EPA Approve the Rules?

To prepare for the planned 2017 review, the Environmental Protection Agency under President Obama produced a 1,200-page assessment last summer of the fuel-economy program.

At the end of November, then EPA head Gina McCarthy made a preliminary determination that there was enough data to lock in the auto industry to the original fuel-economy targets for the 2022 to 2025 model years.

After a shortened public-comment period, McCarthy made the EPA’s “final determination” to proceed with the original fuel-economy standards. The decision was made the month President Obama left office.

What Is the Auto Industry Seeking?

After the January decision, two major trade groups, the Alliance of Automobile Manufacturers and the Association of Global Automakers, urged the new Trump administration to restore the 2017 review. Both argued that McCarthy had short-circuited the process and not given the industry enough time to complete its own extensive research on the benefits and drawbacks of specific fuel-saving technologies.

”Consumers often are making choices that are inconsistent with the long-term success of the current schedule,’’ a group of 18 automaker CEOs wrote to President Trump in February. “Ignoring consumer preferences and market realities will drive up costs for buyers and threaten future production levels, putting hundreds of thousands and perhaps as many as a million jobs at risk.”

Today’s decision shows that the Trump administration agrees with the industry.

"We applaud the Administration’s decision to reinstate the data-driven review of the 2022-2025 standards,” Mitch Bainwol, president & CEO of Auto Alliance, said in a statement. “By restarting this review, analysis rather than politics will produce a final decision consistent with the process we all agreed to.”

Now that the review has been restored, automakers are likely to seek looser standards for the 2022 to 2025 model years. They argue that their sales data show that lower-than-expected gas prices are causing consumers to choose bigger, less fuel-efficient models over hybrids and electric vehicles. That makes it harder for the companies to meet the fuel-economy targets for their entire fleet, they say.

What Do Environmental and Consumer Groups Say?

They believe the automakers’ concerns are overblown. There’s enough flexibility in the regulations, they say, so that companies aren’t penalized if customers decide to buy SUVs and pickup trucks rather than more fuel-efficient cars.

"The White House is following an ideological agenda—anti-regulation and business-friendly,” says Roland Hwang, director of the energy and transportation program at the Natural Resources Defense Council. “It's a very volatile mixture, and it's headed in a dangerous direction. The best thing for consumers, for the automakers and their workers is to leave the agreement as it was."

Consumers Union, the policy and mobilization arm of Consumer Reports, has long urged regulators to set fuel-economy targets at the maximum levels possible, both to improve the environment and to save car owners money.

“The Administration should reconsider today’s action,” says Shannon Baker-Branstetter, policy counsel for Consumers Union. “The EPA finalized the standards after a thorough study of costs and benefits. ... The record shows that they are a reasonable, cost-effective approach to improving fuel efficiency and lowering consumers’ expenses.”

Research by Consumers Union shows that the fuel-economy program hasn’t made cars more expensive, because the cost of new technology has been offset by savings at the gas pump—$3,200 over the lifetime of a car and $4,800 for a truck—even with lower fuel prices. If gasoline prices rise, those savings would be even higher.

“In the last few years, we've seen impressive fuel-economy gains in our testing,” says Jake Fisher, auto testing director for Consumer Reports. “At the same time, performance, safety, and comfort have also improved. These standards have driven new and innovative technology. Uncertainty in the future standards can derail the path the industry is on and undermine those technology investments.”

What Happens Now?

The EPA and the Department of Transportation's National Highway Traffic Safety Administration will fully analyze the data from last summer’s report as well as additional data from automakers and comments from interested stakeholders, including Consumer Reports.

Once the review is completed either this year or next, regulators will have three options: leave the current 2022 to 2025 rules in place (which is what McCarthy did), revise the standards, or propose to eliminate them.

Any attempt to substantially revise or cancel the targets, however, would have to go through a long and complicated rule-making process for federal agencies. And any such move is sure to be challenged in court by environmentalists and consumer advocates.