Robert Baer is a former CIA case officer and the author of several books on the Middle East.

Sometimes, age-old wisdom notwithstanding, the enemy of our enemy turns out not to be our friend. Once, in the mid-1980s, I was handed the portfolio for Libya’s opposition leaders, many of whom were operating out of Khartoum, Sudan. At first, I had only a hazy idea of who Moammar Gaddafi’s opponents were. All I knew for sure was that the Reagan administration wanted Gaddafi to go.

Late one night, I woke up to the sound of the butts of assault rifles pounding my door. Two of my Libyan contacts were on the run from Gaddafi’s assassins and expected me to protect them. We talked most of the night — about Libya, history and Allah. By the time they could safely leave, I had come to understand that the people we’d picked to replace Gaddafi were militant Salafists determined to turn Libya into an Islamic republic. They didn’t succeed then, but you could argue that the people who attacked our diplomatic outpost in Benghazi in September were their linear descendents....