Disputes in economics used to be bounded by a shared understanding of the evidence, creating a broad range of agreement about economic policy. To take the most prominent example, Milton Friedman may have opposed fiscal activism, but he very much supported monetary activism to fight deep economic slumps, to an extent that would have put him well to the left of center in many current debates.
Now, however, the Republican Party is dominated by doctrines formerly on the political fringe. Friedman called for monetary flexibility; today, much of the G.O.P. is fanatically devoted to the gold standard. N. Gregory Mankiw of Harvard University, a Romney economic adviser, once dismissed those claiming that tax cuts pay for themselves as “charlatans and cranks”; today, that notion is very close to being official Republican doctrine.
As it happens, these doctrines have overwhelmingly failed in practice. For example, conservative goldbugs have been predicting vast inflation and soaring interest rates for three years, and have been wrong every step of the way. But this failure has done nothing to dent their influence on a party that, as Mr. Mann and Mr. Ornstein note, is “unpersuaded by conventional understanding of facts, evidence, and science.”