Maybe it’s because the midterm elections went so very well. Maybe it’s because at the White House, politics is the best policy. Maybe it’s because it’s the reign of Karl Rove. An inside look at how the most powerful presidential adviser in a century does what does so well. On a cool Saturday a few days before Christmas last year, Karl Rove showed up in a festive mood at David Dreyer’s house in suburban Washington, D. C., to trim the tree and have a cup of eggnog. Dreyer is a liberal Democrat, formerly the deputy communications director in the Clinton...