Earlier this week, the Environmental Protection Agency announced proposed regulations to curb emissions of ozone, which causes smog, not to mention asthma, heart disease and premature death. And you know what happened: Republicans went on the attack, claiming that the new rules would impose enormous costs.

There’s no reason to take these complaints seriously, at least in terms of substance. Polluters and their political friends have a track record of crying wolf. Again and again, they have insisted that American business — which they usually portray as endlessly innovative, able to overcome any obstacle — would curl into a quivering ball if asked to limit emissions. Again and again, the actual costs have been far lower than they predicted. In fact, almost always below the E.P.A.’s predictions.

So it’s the same old story. But why, exactly, does it always play this way? Of course, polluters will defend their right to pollute, but why can they count on Republican support? When and why did the Republican Party become the party of pollution?

For it wasn’t always thus. The Clean Air Act of 1970, the legal basis for the Obama administration’s environmental actions, passed the Senate on a bipartisan vote of 73 to 0, and was signed into law by Richard Nixon. (I’ve heard veterans of the E.P.A. describe the Nixon years as a golden age.) A major amendment of the law, which among other things made possible the cap-and-trade system that limits acid rain, was signed in 1990 by former President George H.W. Bush.