Tom Steyer, the billionaire environmental activist who spent at least $87 million on the 2016 election, said he can’t begin to estimate how much of his fortune he’ll put toward fighting Donald Trump’s presidency.

“If you ask me can I put a limit on how much I value the health, the safety, the employment and the civil liberties of Americans, there’s no limit to what I think that’s worth,” Steyer, a Democrat, said in an interview Tuesday.

Steyer, the biggest individual political donor in last year’s election, channels most of his money through a network of groups known as NextGen Climate. He’s already combating the president-elect’s cabinet picks and trying to pressure the incoming administration not to roll back environmental regulations.

Trump, who has called climate change a hoax invented by the Chinese to weaken the U.S. economy, has raised concerns among conservationists that he’d roll back environmental protections. He walked back some of his campaign rhetoric, including a promise to abandon the international climate accord reached in 2015 in Paris, in a November interview with The New York Times.

“We don’t know how much of their campaign rhetoric they’re going to try to put into action,” said Steyer. “But this is the most broad-based and dangerous attack on American values certainly that I have ever experienced in my lifetime and much more than I have ever imagined would happen while I’m alive.”

Concerns deepened when Trump announced his picks of Rex Tillerson, the former chief executive of Exxon Mobil Corp., to be his secretary of state, and Scott Pruitt, a longtime opponent of environmental regulations, to head the Environmental Protection Agency. Pruitt, who has led lawsuits against the agency he’s been tapped to head, is an “extreme and dangerous choice,” Steyer said.

Steyer helped create the NextGen Climate network in 2012 after leaving Farallon Capital Management, the hedge fund he co-founded, to devote himself to conservation. In 2016, the group focused on mobilizing young voters around climate change policies. Steyer didn’t rule out using the courts as a way to challenge the Trump administration on environmental matters. “The judicial branch did not disappear,” he said.

Still, despite Trump’s policies, the shift toward cleaner energy isn’t likely to be reversed, because the industry is already firmly established, Steyer said.

Use of renewable energy should outpace fossil fuels, he said, “unless they try to change the rules to somehow advantage dirty energy over clean energy. The industrial logic is in place and I think it’s unstoppable over time.”

In 2016, NextGen spent $7.1 million supporting Hillary Clinton and opposing Trump, Federal Election Commission records show. One of the super-PAC’s biggest expenditures was $13.2 million that it transferred to its affiliate, NextGen California Action Committee, which spent nearly all of that money on ads attacking Trump.

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