The Republican presidential candidates do not support EPA’s new Clean Power Plan. They made that abundantly clear on Monday, when President Obama rolled out the final rule limiting carbon emissions from existing power plants. GOP frontrunners derided the rule with the usual anti-government adjectives: Jeb Bush called it “overreaching” and “irresponsible,” while Ted Cruz said it was “lawless and radical.”

This is as predictable as it is worrisome: Virtually the entire Republican field does not accept climate science and opposes regulating climate pollution. The contrast with the three serious Democratic candidates, all of whom praised the rule and have previously pledged to defend it, could not be starker.

So what will it mean for the Clean Power Plan if a Republican wins the presidency next year? He will get rid of the rule if he can. That would not only cause more climate pollution and conventional pollution; it would undermine the U.S.’s credibility internationally by making it unlikely that we’ll meet our commitments under international climate agreements. In fact, the mere threat of a future Republican administration is already a specter looming over the climate negotiations that will take place in Paris this December.