A third pattern is terrorist “reorientation,” when groups alter tactics, sometimes even entering politics. I lived in Beirut when embryonic precursors of Hezbollah launched the first suicide bombing against an American Embassy, in 1983. After the attack, the seven-story building, which was down the hill from my office, looked like a doll’s house with its façade blown off. Sixty-four died, including some of my friends. Six months later, a bomber drove a Mercedes-Benz truck into the barracks of U.S. Marine peacekeepers in Lebanon. Two hundred and forty-one marines died in the largest loss of U.S. military life in a single incident since the Second World War. I still recall the roar of that bomb waking me up on a balmy October morning, and watching for weeks as the bodies of my countrymen were recovered from under tons of debris.

A decade later, Hezbollah emerged from the underground to run for Parliament, build a network of social services, and greatly expand its support base. Today it has seats in Parliament, Cabinet positions, an alliance with Lebanon’s President, and the largest military force outside the army, as well as hospitals, schools, and welfare agencies. I spent several hours interviewing its leader, Hassan Nasrallah, in 2006, and his deputy, last October. Yet Hezbollah still calls for Israel’s destruction. The United States considers it one of the most dangerous terrorist groups.

“Hezbollah doesn’t rule Lebanon, but it controls it. The message is that terrorism pays. It is translated into power,” Hoffman told me.