Other legal scholars and environmental advocates agreed.

“The loss of Kennedy is not good news for environmental regulation,” said Ann Carlson, a law professor at UCLA and the co-director of the Emmett Institute on Climate Change and the Environment.

The nation’s highest court would now “almost certainly” be more hostile to environmental law than it has been since the founding of the EPA in 1970, said Jonathan Z. Cannon, a law professor at the University of Virginia.

“With the departure of Justice Kennedy, this is no time to mince words: We are in for the fight of our lives,” said Trip Van Noppen, the president of the environmental-legal-advocacy group Earthjustice, in a statement. “Trump intends to fill this Supreme Court vacancy with someone who will put corporations, the wealthy, and the powerful above the rest of us. We must do everything in our power to resist this.”

Experts said that Kennedy’s departure could change the outcome of near-term rulings on three different questions: Can the government fight climate change? How broadly can it regulate clean water? And does the Constitution even allow it to protect endangered species and regulate pollution?

Kennedy provided the crucial fifth vote in Massachusetts v. EPA, which is the most important court case in U.S. climate law. In that decision, the Supreme Court said the EPA could regulate greenhouse gases under the Clean Air Act.

The ruling meant that the president could regulate carbon dioxide and other heat-trapping gases without requiring Congress to pass a new law. It set the stage for President Obama’s broad set of climate-targeted regulations, including his fuel-economy rules for cars and anti-carbon plan for the electricity sector.

Cannon, the University of Virginia law professor whose legal arguments shaped the case, told me that Kennedy’s vote in Massachusetts was “an environmentalist triumph that would not have happened if he had held ranks with other conservatives.”

Had Kennedy not joined with the liberals, then the EPA would likely not have authority over greenhouse gases. With Kennedy gone, this may soon come to pass.

“It’s easy to think about the loss of Kennedy leading to either the repeal of Mass. v. EPA or a serious restriction to the Clean Air Act’s ability to regulate greenhouse gases,” Carlson told me.

Lazarus, the Harvard professor, disagreed that a more conservative court would overturn Massachusetts v. EPA. “I assume [the decision] itself, that greenhouse gases are air pollutants, will hold. That’s a Constitutional law question … I don’t think we’re going to run roughshod over that,” he told me.

But he worried a future court could limit the ability of environmentalists to gain standing. That is, it could seriously restrict the ability of private Americans to sue the federal government for failing to respond to climate change.