...Around dawn on October 23, 1983, I was in Beirut, Lebanon, when a suicide bomber drove a truck laden with the equivalent of twenty-one thousand pounds of TNT into the heart of a U.S. Marine compound, killing two hundred and forty-one servicemen. The U.S. military command, which regarded the Marines’ presence as a non-combative, “peace-keeping mission,” had left a vehicle gate wide open, and ordered the sentries to keep their weapons unloaded. The only real resistance the suicide bomber had encountered was a scrim of concertina wire. When I arrived on the scene a short while later to report on it for the Wall Street Journal, the Marine barracks were flattened. From beneath the dusty, smoking slabs of collapsed concrete, piteous American voices could be heard, begging for help. Thirteen more American servicemen later died from injuries, making it the single deadliest attack on American Marines since the Battle of Iwo Jima.

Six months earlier, militants had bombed the U.S. embassy in Beirut, too, killing sixty-three more people, including seventeen Americans. Among the dead were seven C.I.A. officers, including the agency’s top analyst in the Middle East, an immensely valuable intelligence asset, and the Beirut station chief.

There were more than enough opportunities to lay blame for the horrific losses at high U.S. officials’ feet. But unlike today’s Congress, congressmen did not talk of impeaching Ronald Reagan, who was then President, nor were any subpoenas sent to cabinet members. This was true even though then, as now, the opposition party controlled the majority in the House. Tip O’Neill, the Democratic Speaker of the House, was no pushover. He, like today’s opposition leaders in the House, demanded an investigation—but a real one, and only one. Instead of playing it for political points, a House committee undertook a serious investigation into what went wrong at the barracks in Beirut. Two months later, it issued a report finding “very serious errors in judgment” by officers on the ground, as well as responsibility up through the military chain of command, and called for better security measures against terrorism in U.S. government installations throughout the world.

In other words, Congress actually undertook a useful investigation and made helpful recommendations. The report’s findings, by the way, were bipartisan. (The Pentagon, too, launched an investigation, issuing a report that was widely accepted by both parties.)...