By Robinson Meyer, The Atlantic.

In the weeks after the election of Donald Trump, friends and journalists called Deborah Sivas with roughly the same question: How bad could things get?

Sivas is a professor of environmental law at Stanford University, and she has decades of experience working as a litigator for environmental-rights groups. She knows how hostile new presidents can overturn green protections and she knows how lawsuits from friendly states and nonprofits can shore up those rules.

So when reporters asked about the fate of signature Obama-era issues—the Clean Power Plan, the Paris Agreement, the Dakota Access pipeline—she replied that they should focus on an issue with less name recognition. It seemed likely, she said, that the Trump administration and its allies in the car industry would attack California’s ability to regulate greenhouse-gas pollution from car tailpipes.

This may sound niche. But if Trump revoked the special federal waiver that gives California this power, it could hinder the ability of the United States to address climate change for decades to come, she said.

It now appears that her instincts were correct. On Saturday, The New York Timesreported that Scott Pruitt, the new administrator of the U.S. Environmental Protection Agency, was exploring how to withdraw this waiver from California. The announcement could come later this week, when the Trump administration begins to roll back nationwide regulations on pollution from car tailpipes.

“We hear a lot about Paris and the Clean Power Plan, but this [waiver] is a big part of it too,” Sivas told me. “These were the years—2017 and going forward—when the curve was supposed to bend a lot on car emissions.”

The probable withdrawal has so far avoided attracting significant activist attention, perhaps because the idea of the waiver is difficult to explain or because at first glance it appears to be a local issue affecting only Californians.