When Donald Trump gave his big energy speech in North Dakota last week, he recited a well-established set of Republican talking points in favor of coal, oil, and gas and against climate action. But he also made a relatively new and particularly dishonest claim, one that he repeated the next day in California: that he will promote clean air and clean water.

As conservatives have grown more extreme in their opposition to regulating climate pollution, they’ve struggled to paint themselves as supporters of a clean environment. This is a problem, as most voters value breathable air and drinkable water.

Some leading Republicans have tried talking their way around this obstacle by conflating carbon emissions with other forms of air pollution. Rand Paul, for example, has deliberately confused the two, arguing that climate activists are “hysterics” because “pollution” is “actually much better now.” Conventional air pollution, such as nitrogen oxides and sulfur dioxide, is indeed lower than it was before passage of the Clean Air Act, but carbon pollution is much worse.