THE man spoke in "a low, hard tone," recalled the operator on duty at the Capitol switchboard. His message was equally ominous: "This building will blow up in 30 minutes. You will get many calls like this, but this one is real." At 1:32 a.m., 33 minutes after the phone warning, a dynamite bomb demolished an unmarked, out-of-the-way men's room in the Capitol basement. It was only the fourth time in history that protesters had brought violence to the domed symbol of U.S. democracy.*
The explosion occurred in the original section of the Capitol, begun during George Washington's term in office and...