In the Biden administration, the American environmental movement reached what many of its supporters considered an apex. Congress passed the largest ever federal law to combat climate change. Coal-burning power plants were shutting down. Hundreds of billions of dollars of federal investment in renewable energy, batteries and electric vehicles was beginning to flow.

But in just months, President Trump has attacked much of that work.

The Biden-era climate law, known as the Inflation Reduction Act, is in tatters. The White House is trying to revive coal, the dirtiest fossil fuel, while boosting oil and gas and hindering solar and wind power. And it is weakening or trying to scrap environmental policies and regulations, some dating to 1970.

The abrupt reversal in fortunes has led to a moment of crisis for the environmental community. “The morale is destroyed,” said Ramon Cruz, a former president of the Sierra Club. “I won’t try to sugar coat it. This is a generational loss.”

After a series of stinging defeats and other challenges, some prominent environmental groups are adrift. This week, the Sierra Club’s executive director was fired after a rocky tenure in which he oversaw several rounds of layoffs and clashed with employees. Greenpeace is facing a $670 million legal verdict that could put its future at risk. Rewiring America, a nonprofit group that works to electrify buildings, has slashed nearly a third of its staff.

Actions by the Trump administration and the Republican-led Congress have set the environmental movement back years, activists said. Chief among them has been the passage Mr. Trump’s domestic policy bill, which curtailed many of the core elements of the Inflation Reduction Act.

“With one election and one bill, most of the signature climate work that organizations, advocates and movements have been working toward is largely undone,” said Ruthy Gourevitch, a policy director at the Climate and Communities Institute, a progressive research organization.

A change in approach

The Trump administration’s assault on climate policies has pushed some environmental groups to shift their focus away from federal policy. Manish Bapna, president of the Natural Resources Defense Council, said his group was redoubling its efforts in state and federal courts and expanding its advocacy at the state level and internationally.

“We recognize that the United States is much larger than Washington, D.C., and the world is much larger than the United States,” Mr. Bapna said.

In the fiscal year that ended in June, the NRDC saw its second highest fund-raising total ever, according to Mark Drajem, a spokesman. (Its best year was 2021.) It is increasing its focus in states like Georgia and Ohio, where it sees opportunities to accelerate solar energy. It is helping to support a Vermont law that would hold fossil fuel companies responsible for climate damage. And the group is expanding its work in India and beginning to work on projects in Africa.

Some hope the environmental movement finds lessons in its recent losses.

Tom Steyer, the billionaire investor who has supported past efforts to mobilize climate voters and pass climate initiatives on state ballots, said the lesson of the 2024 election is that the public wants solutions that have immediate economic effects.

“If we want to win, we need a fundamental recalibration,” Mr. Steyer recently wrote on Facebook. “Climate can no longer be a separate cause. It must be the context for making people’s lives better. It has to feel like relief. Like opportunity.” For example, he wrote, clean energy must mean lower electric bills.

During the first Trump administration, the most successful challenges to the president’s attempts to roll back environmental regulations were in the courts. Upon taking office in 2020, President Joseph R. Biden Jr. restored and strengthened many regulations protecting air, water and the climate.

When Mr. Trump was elected to a second term, lawyers at environmental groups anticipated he would dial up the pressure. But the speed and intensity of the fight has exceeded their expectations, said Abigail Dillen, president of Earthjustice, a nonprofit environmental-law group.

As a result, there has been more deliberate coordination with other environmental groups during President Trump’s second term, Ms. Dillen said. In June, Earthjustice, the Southern Environmental Law Center, the Public Rights Project and Lawyers for Good Government filed a class-action suit on behalf of 350 groups that lost funding under the Inflation Reduction Act.

Earthjustice has opened 96 legal actions against the Trump administration this year, including lawsuits as well as technical comments on proposed regulatory changes. That’s nearly three times the amount it initiated during the first six months of Mr. Trump’s first term.

It has had some wins. On Thursday, a federal judge in Washington ordered the Agriculture Department to reinstate grants for farmers and nonprofits that had been terminated. The groups were represented by Earthjustice and two other legal nonprofits, FarmSTAND and Farmers Justice Center.

The movement’s challenges

Still, environmental groups are facing many challenges, including one major lawsuit, internal disagreements and the threat of being targeted by the Trump administration.

Greenpeace lost a lawsuit in March after being sued over allegations it defamed Energy Transfer Partners, the company behind the Dakota Access Pipeline. Kelcy Warren, the company’s chairman, was a major donor to Mr. Trump’s 2024 campaign.

His company accused Greenpeace of an “unlawful and violent scheme” to incite demonstrations to stop the project. Greenpeace has maintained that it played a minor role promoting peaceful protest and that its actions were protected by the First Amendment.

Greenpeace now faces the prospect of nearly $670 million in damages if it loses on appeal, with its U.S. arm responsible for the vast majority of that amount. That prospect has led Greenpeace to pursue “voluntary separation” agreements with 22 employees, roughly 20 percent of its head count.

But Sushma Raman, the interim executive director of Greenpeace USA, said donations to the organization have remained strong. She said the group was relying on “the power of our mission, the power of the movement, the power of our supporters to keep focusing ahead.”

The Sierra Club, one of the nation’s oldest environmental groups, has been rocked by a leadership crisis. Ben Jealous, who took over as executive director in 2023, was fired on Monday after a year of tension between Mr. Jealous and local chapters, employees and the organization’s union. Mr. Jealous had inherited a substantial budget deficit when he joined the organization, which has an annual revenue of more than $100 million. The group went through several rounds of layoffs, depressing morale.

Mr. Jealous said he planned to fight the termination.

At the same time, the Sierra Club and three other environmental groups are facing a defamation lawsuit by Exxon Mobil in federal court in Texas.

Funding struggles

Another setback has been the Trump administration’s cancellation of billions of dollars in grants for some environmental organizations. The administration has attempted to claw back $27 billion in grants for clean energy and efficiency projects through the Greenhouse Gas Reduction Fund, which is part of the Inflation Reduction Act.

Rewiring America was slated to receive $490 million of those grants, a significant bump for an organization that reported $621,000 in revenue in 2023. But when Mr. Trump retook the White House, the funds were frozen at the administration’s request. In May, Rewiring America cut 28 percent of its staff.

Across the environmental movement, there is a widespread sense that money from donors will be harder to come by in the years ahead. Some funders and nonprofits have stepped in to help environmental groups that lost federal support and, in some cases, have lent them staff members.

It’s unclear whether funding trends have changed in recent months. Large foundations do not typically change their spending strategies quickly. And nonprofit organizations do not report fund-raising results in real-time.

“It’s going to be a hard time to find brand-new climate funders,” said Randall Kempner, executive director of the Climate Philanthropy Catalyst Coalition, an umbrella organization of environmental donors.

Breakthrough Energy, the Bill Gates-backed group focused on promoting clean energy, shuttered its D.C. lobbying shop in March, laying off staff and cutting off funding for a number of related groups.

With a White House working to thwart climate action, Mr. Gates made the calculation that his philanthropic dollars would be better spent elsewhere, including helping fill the void left by the dissolution of the U.S. Agency for International Development, according to people familiar with his thinking who spoke on the condition of anonymity because they were not authorized to speak publicly.

Mr. Gates is investing directly in climate technology, including a next generation nuclear plant in Wyoming that would generate electricity without emitting greenhouse gases. He declined to comment.

Mr. Steyer, through his investment firm, Galvanize Climate Solutions, is also putting his money into clean energy projects and said he invests differently than other climate donors. “We’re not funding any suits,” he said, referring to legal challenges against the Trump administration. “We are basically trying to create better things that provide tangible benefits now.”