Associate Justice Anthony Kennedy’s retirement from the U.S. Supreme Court has set off a political firestorm over his replacement, opening the door to new debate about the most volatile social issues—from abortion and guns to voting rights and same-sex marriage.

Add at least one more lightning rod issue to the list: the environment.

Pres. Donald Trump has already said he will pick Kennedy’s replacement from the same list of conservative judges circulated before the 2017 nomination of Associate Justice Neil Gorsuch. Trump’s new pick is set to tip the balance of the Court on a range of critical issues.

That means several marquee environmental laws could be reshaped or upended, according to legal scholars. These include measures to safeguard wildlife, combat climate change and determine which waterways are federally protected. This fall the new Court will get its first chance to hear a science-heavy environmental conflict with Weyerhaeuser Company v. United States Fish and Wildlife Service, a case testing the scope of habitat protections under the Endangered Species Act (ESA)..

Kennedy, known as the Court’s swing vote, has a mixed record on environmental cases. But for decades he played a central role in deciding them, including a landmark climate change decision in which he provided the tie-breaking vote finding the U.S. Environmental Protection Agency could regulate greenhouse gases. Chris Robertson, a law professor at the University of Arizona, says he is concerned that an ideological replacement justice could reinforce what he calls a growing culture of “science denialism.” He adds, “Kennedy’s demeanor could sometimes be persuaded by facts and evidence and science. With everything from vaccine mandates to the environment to public health to technological changes, it would be worrisome if the replacement is an ideological dogmatist who is not interested in how things work in the real world.”

Over the past weekend Trump doubled down on plans to make his pick by July 9, which would officially set in motion a nasty partisan fight on Capitol Hill ahead of the November midterm elections. Here is how several environmental issues could be affected by a high court tilted with two of Trump’s conservative picks:

Endangered Species Act

A nearly extinct frog is at the center of a case that could determine the extent to which the federal government can designate private land as a critical habitat to protect an endangered species. The dusky gopher frog (Lithobates sevosus), found only in four locations in southern Mississippi, requires a specific habitat to survive. Federal officials had established new breeding populations in Mississippi, but the frog species had apparently been eradicated from southeastern Louisiana and parts of Alabama, where it had historically been found. The U.S. Fish and Wildlife Service has identified 1,500 forested acres in Louisiana as a candidate for a protected area to establish a new dusky gopher frog population, even though the frogs do not currently live there.

Timber giant Weyerhaeuser Co. currently owns the land in question and sued the federal government, arguing the critical habitat designation infringes on the company’s ability to use the land as it sees fit. Weyerhaeuser has argued that the frogs have not lived in the state since 1965 and cannot reacclimate without major changes to the land.

The timber company’s challenges have failed in lower courts, and Kennedy had previously ruled the government could regulate private land under the ESA. But a newly conservative-aligned Court could limit the ESA’s reach, says Patrick Parenteau, an environmental lawyer at Vermont Law School. “It is likely it will come out 5–4 against the frog, and Kennedy’s replacement could very well make the difference in the outcome of this case,” says Parenteau, who is filing a friend of the court brief in the case on behalf of nearly two dozen environmental lawyers. A Supreme Court ruling that favors the timber company could mean less federal protection for threatened and endangered species, he says. “Historic habits are being altered in a way that they will no longer be suitable for many species, and that means they’re going to have to move,” he adds. “Some of them will have to move to a habitat that is not suitable today and needs to be restored.”

Clean Water Act

Kennedy’s retirement also significantly alters the landscape for another pressing environmental question: How broadly can the federal government protect and regulate streams and waterways?

The Court last examined the Clean Water Act, which allows the government to protect “navigable waters” from pollution, in the 2006 case Rapanos v. United States. A debate over how to define navigable waters has persisted, creating a murky legal situation for wetland protection in the dozen years since. When the case was heard, conservative justices led by Antonin Scalia took the approach federal protection extended only to “relatively permanent” waters and wetlands that have a continuous surface connection to larger rivers and streams. That excluded most small wetlands and waterways. “Any biologist would tell you that is a crazy definition if you’re trying to protect aquatic life,” says Thomas McGarity, an environmental law professor at The University of Texas at Austin.

But Kennedy, in what some argue was his most significant environmental opinion, served as the swing vote in the case by declaring the Clean Water Act covers any wetlands or small waterways with a “significant nexus” to larger waters downstream. Kennedy’s opinion and significant nexus test became the basis for a contentious Obama-era Clean Water regulation revision of what is known as “Waters of the United States,” or WOTUS, defining which wetlands and small waterways are federally protected.

The Trump administration, however, has revoked the Obama water rule and is currently working to replace it with a weaker version, based on Scalia’s definition from the 2006 case. It could take years for related litigation to reach the nation’s highest court. But when it does, “if you put a different justice there instead of Kennedy the Court will probably accept the Trump administration definition,” McGarity says.

Massachusetts v. EPA

In the 2007 case Massachusetts v. Environmental Protection Agency Kennedy cast the deciding vote in a 5–4 decision determining the EPA could regulate greenhouse gases as air pollutants. This is regarded as a landmark case that set the stage for several Obama administration regulations targeting climate change. “The ruling really led to the obligation of the EPA having to look the science in the eye,” says Lisa Heinzerling, a law professor at Georgetown University.

A more conservative Court could curtail this ruling's reach—or repeal it altogether—says Vermont’s Parenteau. Two of the Court’s conservative justices have already called for the decision to be overturned. “With the new Court you could see Mass. v. EPA overruled just the same way we could see Roe v. Wade overruled,” Parenteau says, referring to the decision that guaranteed a woman’s right to abortion. “It was Kennedy’s vote that kept [Massachusetts v. EPA] alive.”

Heinzerling says “there has already been damage done to Massachusetts v. EPA,” but it is not clear that a more conservative Court would strike the law in its entirety. “I don’t know what some of these justices think in their heart of hearts about scientific evidence, but I do know they have been willing to cast scientific evidence aside in their service of a deregulatory agenda,” Heinzerling adds, referring to the four justices who voted against the EPA having the authority to regulate greenhouse gases in the landmark 2007 case. “They are willing to ignore science or skew their view of legal principles to comport with their own political worldview.”