A rule of the modern age: all confident, reelected presidents trip up in the second term. LBJ was sunk by Vietnam. Reagan faced Iran-Contra. Bill Clinton had his comeuppance with Monica. George W. Bush was overwhelmed with the Iraqi insurgency and Katrina. And Obama will have his as well, obsequious media or not. Supposedly fundamental partisan swings of an era usually prove transitory: LBJ’s landside led to Nixon four years later, whose landslide then led to Carter in 1980, whose supposed new politics of humility and apology led to Reagan, whose small government-paradigm shift nonetheless by 1992 gave us Clinton,...