President Obama, reacting with the same horror as many Americans to a grisly video of a bloody, dying man in Minnesota who was shot by the police, begged the nation to confront the racial disparities in law enforcement while acknowledging the dangers that officers face. “When incidents like this occur, there’s a big chunk of our citizenry that feels as if, because of the color of their skin, they are not being treated the same, and that hurts, and that should trouble all of us,” Mr.