SAN JUAN, Puerto Rico -- Puerto Rican police tightened security at federal buildings and Sen. Hillary Rodham Clinton canceled a visit to the island amid fears the killing of a Puerto Rican nationalist in an FBI shootout could lead to a resurgence of pro-independence violence. Police chief Pedro Toledo acknowledged the potential for unrest, saying the death of Filiberto Ojeda Rios had generated "rancor and rage." Ojeda Rios, 72, was shot to death Friday by FBI agents who came to arrest him at his farmhouse in southwestern Puerto Rico for the 1983 armed robbery of a Wells Fargo depot in...