David Brooks: “All across the nation, there are mainstream Republicans lamenting how the party has grown more and more insular, more and more rigid. This year, they have an excellent chance to defeat President Obama, yet the wingers have trashed the party’s reputation by swinging from one embarrassing and unelectable option to the next: Bachmann, Trump, Cain, Perry, Gingrich, Santorum. But where have these party leaders been over the past five years, when all the forces that distort the G.O.P. were metastasizing?”

