DALLAS — When President John F. Kennedy’s motorcade left the airport here shortly before noon on Nov. 22, 1963, the man seated in the lead car was the county sheriff, Bill Decker, 65, a storied Texas lawman who led the hunt for Bonnie and Clyde. Fifty years later, the badge belongs to Lupe Valdez, 66, the daughter of Mexican migrant farmworkers. She is the only sheriff in America who is an openly gay Hispanic woman. Voters re-elected Sheriff Valdez, a Democrat, to a third term last year.

Dealey Plaza — where the darkest day in Dallas history unfolded 40 minutes after the motorcade began — looks eerily similar to what it was then, the sixth-floor corner window of the former Texas School Book Depository still cracked open slightly. But Dallas itself is almost as different as Bill Decker is from Lupe Valdez.

And the tension between past and present has unleashed a wave of citywide self-reflection a half-century later in a distinctly American place that is part Dallas Cowboys, part Texas excess and part urban melting pot, where the public school students come from homes where 70 languages are spoken. Painful, embarrassing memories of the angry anti-Washington culture that flourished here 50 years ago — and now seems a permanent part of the national mood — have resurfaced, confronting Dallasites daily....