California Gov. Jerry Brown (D) came out swinging last week on climate change, vowing to protect the state’s environmental policies from President-elect Donald Trump.

Positioning the Golden State as the country’s liberal champion, Brown noted that California has triumphed before on green issues, like pushing for the nation’s toughest restrictions on vehicle emissions. The state’s tailpipe pollution rule later became the national one in an agreement certified during the Obama administration.

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“There is a movement now among some of the more progressive states to use the courts to some extent for those kind of purposes … to stopping the watering-down of regulations,” said Deborah Sivas, professor of environmental law at Stanford University. “They’re going to kind of peel a page out of that playbook.”

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“I think Brown would want to lead the challenge very aggressively” on opposing that, Sivas said.