Environmental groups and progressive states are vowing to battle President Trump in court over his push to repeal federal climate protections, and experts are warning that the battles ahead will be slow and protracted.

An executive order on energy regulations signed by Trump on Tuesday takes direct aim at President Obama’s landmark climate rule, the Clean Power Plan, which would limit greenhouse gas pollution from power plants beginning in 2022.

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“It’s a more cautious and well thought-out executive order than the ones we’ve seen from Trump so far,” said Michael Wara, an energy and environmental expert at Stanford Law School.

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“It doesn’t actually do anything,” Wara said. “What it sets in place is a process to review the rules promulgated by the Obama administration.”