Walker has implemented an impeccably conservative agenda in a state that has gone Democratic in seven straight presidential elections. Unlike Mitt Romney, or, for that matter, John McCain, he is beloved by the conservative base, but he has the mien of a mainstream candidate, not a favorite of the fringe. His boosters, who include numerous greenroom conservatives in Washington and major donors around the country, such as the Koch brothers, see him as the rare Republican who could muster broad national support without yielding a millimeter on doctrine.

This interpretation of Walker’s appeal could hardly be more flawed. He has succeeded in the sort of environment least conducive to producing a candidate capable of winning a national majority. Over the past few decades, Walker’s home turf of metropolitan Milwaukee has developed into the most bitterly divided political ground in the country—“the most polarized part of a polarized state in a polarized nation,” as a recent series by Craig Gilbert in the Milwaukee Journal Sentinel put it. Thanks to a quirk of twentieth-century history, the region encompasses a heavily Democratic and African American urban center, and suburbs that are far more uniformly white and Republican than those in any other Northern city, with a moat of resentment running between the two zones. As a result, the area has given rise to some of the most worrisome trends in American political life in supercharged form: profound racial inequality, extreme political segregation, a parallel-universe news media. These trends predate Walker, but they have enabled his ascent, and his tenure in government has only served to intensify them. Anyone who believes that he is the Republican to save his party—let alone win a presidential election—needs to understand the toxic and ruptured landscape he will leave behind.