On Friday, President Trump was named the lead defendant in a lawsuit brought by 21 US students – one as young as nine – against the US government.

The case, Juliana v. United States, was first filed in 2015 with President Barack Obama listed as lead defendant, so the switch to Mr. Trump is largely procedural.

But the plaintiffs are seeking a court order that will compel the US government to phase out fossil fuels. With the change from Mr. Obama to Trump, they’re now taking on an administration that looks askance at climate science.

This marks the latest shift in a years-long legal campaign that aims to move beyond political inaction on climate change by establishing a Constitutional right to a stable climate.

"The US is most responsible for climate change, so it's really the most important case in the world right now on the issue," said Julia Olson, lead counsel for the plaintiffs.

The group sponsoring this lawsuit, Our Children’s Trust, has been attempting to litigate climate-change action since 2011, when young plaintiffs affiliated with the group filed lawsuits or regulatory petitions in all 50 states.

While these cases differed in their specifics, they all sought to apply the public trust doctrine – the concept that the government owns and must maintain natural resources for the public’s use – to the atmosphere, and, by extension, compel state governments to implement policies that would phase out fossil fuels and thus drastically reduce carbon dioxide emissions.

The group has had some success. In September 2016, after the Massachusetts Supreme Judicial Court sided with the group, Gov. Charles Baker issued an executive order directing the state government to establish emissions-reductions regulations by August 2017, and prepare a "comprehensive energy plan" within two years.

But elsewhere, judges saw greenhouse-gas reductions as a matter for the legislatures, not the courts.

In New Mexico, for instance, the state appeals court ruled that, "where the State has a duty to protect the atmosphere under ... the New Mexico Constitution, the courts cannot independently regulate greenhouse gas emissions in the atmosphere as Plaintiffs have proposed.”

Robert L. Wilkins, judge for the US District Court in the District of Columbia, echoed these thoughts on the federal level, ruling that "federal courts have occasionally been called upon to craft remedies that were seen by some as drastic.... But that reality does not mean that every dispute is one for the federal courts to resolve, nor does it mean that a sweeping court-imposed remedy is the appropriate medicine for every intractable problem.”

But last November, a federal judge in Oregon ruled that a case brought by Kelsey Juliana and 20 other young plaintiffs could proceed to trial. Judge Ann Aiken grounded her ruling in the Fifth Amendment's promise that "no person ... shall be deprived of life, liberty, or property, without due process of law."

She wrote, "Where a complaint alleges governmental action is affirmatively and substantially damaging the climate system in a way that will cause human deaths, shorten human lifespans, result in widespread damage to property, threaten human food sources, and dramatically alter the planet's ecosystem, it states a claim for a due process violation."

The trial will begin in Judge Aiken’s courtroom later this year. The plaintiffs' attorney, Ms. Olson, is confident that the case will proceed to – and win in – the Supreme Court, as reported by Slate’s Eric Holthaus.

But legal experts caution that the trial and appeals process could take years, and that the Trump administration will likely want to drag it out for as long as possible.

And even the landmark legal victory sought by Our Children’s Trust might not mean the end of the story. The decades-long struggle to desegregate cities through busing and other programs revealed the difficulties of translating court orders into workable public policy – especially when doing so impacts citizens' day-to-day lives.

Even so, after years of legislative inaction on the issue, environmental activists are looking for outside-the-box solutions, and many see new hope in Our Children’s Trust.

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As Michael Burger, executive director of the Sabin Center for Climate Change Law at Columbia University, told Slate, "There is no question that [Judge Aiken’s] decision, in both its eloquence and its bold declaration of a new constitutional right, breaks new ground."

[Editor's note: An earlier version of this story misstated the goal of Juliana v. United States, which is to phase out fossil fuels entirely.]