Right-leaning legal activists along with Elon Musk’s artificial intelligence company have brought sweeping challenges against a cornerstone of legal enforcement in the United States: the right of private groups, people and local governments to sue over violations of many major laws.

Their argument, supported by the Trump administration, is that the Constitution reserves tremendous power for the president and federal agencies to decide how — or whether at all — to enforce federal law. They contend Congress should never have handed that power to others through so-called citizen suits that are part of environmental, campaign finance and certain other laws.

Environmentalists say it would be devastating to lose this essential, decades-old tool that is used to impose fines and halt lawbreaking by bad actors. Citizen suits, for example, have extracted millions from heavily polluting oil and gas operations, and ensured that lead pipes in Flint, Michigan, would be removed after its water crisis.

Legal experts say four pending federal cases — one of them filed last week — are moving forward at a time when the conservative majority on the Supreme Court gives opponents of citizen suits a greater chance than ever of success. The hard part for those opponents now is winning early federal cases and creating disagreement between the country’s appeals courts, which may help convince the Supreme Court the issue is important enough for a nationwide ruling.

Back in 2000, a Supreme Court opinion opened the door for that possibility.

“Many of us who worked in this area have been waiting basically 26 years for this shoe to drop,” said Richard Lazarus, a Harvard professor with decades of experience in environmental law.

Lazarus was referring to former moderate Justice Anthony Kennedy’s comments in a Clean Water Act case that citizen suits raised “difficult and fundamental” questions about whether they improperly dilute executive power. The late conservative Justice Antonin Scalia wrote in a dissenting opinion in the same case that citizen suits turn “over to private citizens the function of enforcing the law.” He avoided explicitly saying they were constitutional.

“The court is more like Scalia’s court since he died than it ever was when he was there,” said Lazarus.

He observed that those who lost cases where Scalia dissented are rushing back to today’s court hoping for a more favorable result.

The critical issue for citizen suits is who — the government or private citizens — collects fines and has control. A person filing a citizen suit must tell the government ahead of time. The government can stop the suit if it sufficiently pursues the case itself, but its options are limited and the person suing can stay involved. Citizen suits can force compliance with the law and result in fines, which go to the U.S. Treasury.