Now we know, thanks to The Afghanistan Papers published in The Washington Post this past week, that U.S. policymakers doubted almost from the start that the two-decade-long Afghanistan war could ever succeed. Officials didn’t know who the enemy was and had little sense of what an achievable “victory” might look like. “We didn’t have the foggiest notion of what we were undertaking,” said Douglas Lute, the Army three-star general who oversaw the conflict from the White House during the administrations of George W. Bush and Barack Obama. And yet the war ground on, as if on autopilot. Obama inherited a...