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“Steve Bullock is the most important person on the planet,” Robert Frank, the economist and author, recently wrote to me in an email.

Bullock is the populist Democratic governor of Montana who’s running a lackluster campaign for president. But he’s so popular in Montana, despite its deep conservatism, that he is the only Democrat with any reasonable chance of beating the state’s incumbent Republican senator, Steve Daines, next year. That’s why Frank thinks Bullock is the most important person on the planet.

“The window of opportunity for effective action on the climate crisis is rapidly closing,” Frank wrote. “Absent robust measures to curb greenhouse gases, climate scientists forecast steadily more frequent and intense storms, droughts, flooding, and wildfires. Alone among major political parties worldwide, Republicans have refused even to admit the existence of climate change, much less enact meaningful legislation for dealing with it.” And seemingly the only way the United States will take meaningful climate action in the next couple years is if the Democrats control both Congress and the White House.