How can you tell Jon Huntsman, President Obama’s former ambassador to China, is serious about his burgeoning Republican presidential campaign? He’s flip-flopping on cap-and-trade.

Caring about climate change was one of the issues that helped separate Huntsman from the knee-jerk conservatives currently dominating the GOP field, bolstering the impression that he’s a moderate. He even appeared in a nationally-televised Environmental Defense Fund commercial, urging Congress to pass legislation capping greenhouse gases.

And yet, Huntsman backpedaled when the subject came up during an interview with Time magazine.

Already he’s in primary-season mode … junking his support for the regional cap-and-trade carbon-emissions pact he and former California governor Arnold Schwarzenegger once championed. “It hasn’t worked,” he says now, “and our economy’s in a different place than five years ago.”

Yes, and the climate crisis is in a worse place than five years ago.

For those keeping score at home, Huntsman joins a long list of national GOP leaders who suddenly discovered their opposition to cap-and-trade just a few years after endorsing it. The list includes Mitt Romney, Tim Pawlenty, Newt Gingrich, Mike Huckabee, and Sarah Palin, all of whom endorsed the climate policy — some as recently as 2008 — and all of whom have reversed course to make right-wing activists happy.

As for why so many have made the transition from sensible to reckless so quickly, I still think Kevin Drum’s recent item on this rings true.

The answer isn’t very complex. Four years ago, in the wake of Al Gore’s Inconvenient Truth and growing public concern about global warming, corporate America felt that some kind of action on greenhouse gases was probably inevitable. And if it was inevitable, then cap-and-trade was their best bet. From their point of view it probably looked less threatening than a flat carbon tax, which is harder to game than cap-and-trade, and less costly than flat mandates from the EPA. So they got on board, and Republicans got on board with them.

But then a couple of years ago public concern over global warming started to wane and it became less obvious that action on greenhouse gases really was inevitable. So instead of settling for cap-and-trade as their least worst alternative, they decided to fight instead for their first best alternative: doing nothing. And once again, Republicans got on board with them.

This is also made easier by the lack of public demand. When most Americans — even most Republicans — agreed that the climate crisis was a serious threat, prominent GOP officials felt the need to take the issue seriously and present ideas to address the problem.

But now that the mainstream cares less, and the Republican rank-and-file has been told by Fox News that climate science is a communist conspiracy, party leaders no longer feel the need to even keep up appearances.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.