According to Public Policy Polling, only 21 percent of Republican voters in Iowa believe in global warming (and only 35 percent believe in evolution). Within the G.O.P., willful ignorance has become a litmus test for candidates, one that Mr. Romney is determined to pass at all costs.

So it’s now highly likely that the presidential candidate of one of our two major political parties will either be a man who believes what he wants to believe, even in the teeth of scientific evidence, or a man who pretends to believe whatever he thinks the party’s base wants him to believe.