Richard Perry/The New York TimesKalustyan's, a market at 123 Lexington Avenue, is the only building still standing where a president was sworn in: Chester A. Arthur. Forlornly unidentified and altogether forgotten, these sites have been literally lost to history. ...on West 125th Street...nothing marks the place where the Rev. Dr. Martin Luther King Jr. was stabbed in 1958. Then there is the spot on Fifth Avenue where Winston Churchill, crossing against the light, was struck by a car in 1931 and nearly killed. snip Andrew Carroll, 39, an amateur historian, is embarking this week on a 50-state journey to...