Hillary Clinton and New York Mayor Bill de Blasio sparked controversy at an event on Saturday with a racially charged joke. Clinton and de Blasio were joined onstage by Leslie Odom Jr. in costume as Aaron Burr, whom he plays in the hit Broadway musical Hamilton. Clinton thanked de Blasio for his endorsement–which many pointed out came rather late in the game–and ribbed him, “Took you long enough.” The mayor replied, “Sorry, Hillary, I was running on C.P. time.” The abbreviation refers to the stereotype of “Colored People time,” and several people in the audience could be heard gasping or...