WASHINGTON - On this snow-draped Inauguration Day in Washington, a few people on Capitol Hill were thinking about the worst: a catastrophic attack that could kill or incapacitate most members of Congress, the president, the vice president and the cabinet. advertisement The unseen presence at this first inauguration since Sept. 11, 2001, is al-Qaida, whose terrorists showed three years ago how capable they were of killing thousands of Americans in one place at one time. At 9:30 on inauguration morning, in his office in the Longworth Building, a short walk from where the president would soon take his oath, Rep....