For all his partisan animus toward President Obama, it is still shocking to see the Senate’s majority leader, Mitch McConnell, urge the nation’s governors to undermine the Obama administration’s efforts to regulate power plant emissions of carbon dioxide, the main greenhouse gas responsible for global warming.

Mr. McConnell, a Kentucky Republican who seems to hold Mr. Obama personally responsible for what has been the decades-long decline of coal jobs in his state, expressed his defiance in an op-ed article Wednesday in The Lexington Herald-Leader.

The administration has proposed regulations aimed at limiting emissions. Mr. McConnell urged the governors not to cooperate with a joint rule-making process aimed at developing final regulations under which Washington will set emissions targets while giving states flexibility to implement them. Sabotaging this process, he says, will give the courts time to find the plan illegal or give the Senate time to figure out a way to block it. “Without your support,” he said, the administration “won’t be able to demonstrate the capacity to carry out such political extremism.”

Mr. McConnell’s call to governors to sit on their hands is a travesty of responsible leadership. What he calls “extremism” is the administration’s eminently reasonable goal to reduce America’s greenhouse gas emissions 26 percent below 2005 levels by 2025. That pledge is the centerpiece of the climate strategy Mr. Obama hopes to present to the world in Paris in December, at the next climate summit. In that sense, Mr. McConnell’s defiance is more than the usual states’ rights rhetoric that Republicans have used to challenge other initiatives. It is an attack on this country’s credibility as a leader in the fight against climate change.