The “Green New Deal” has hit the political mainstream in a way most environmental issues never do.

It all started with the quixotic candidacy of Rep. Alexandria Ocasio-Cortez (D-N.Y.) and a little-known environmental group called the Sunrise Movement, but now cable news routinely runs segments about it and at least six Democratic presidential candidates have endorsed it.

Ocasio-Cortez officially introduced her resolution with Sen. Ed Markey (D-Mass.) earlier this month, formally laying out the plan in broad, vague steps. Now the race is on to define what it is and where it goes.

Senate Majority Leader Mitch McConnell (R-Ky.) is plotting a step in that fight, with his chamber set for a vote on the resolution as soon as…