The Tuesday tweet was not the first time Trump had used his favorite social media platform to jab at Chicago's homicide rate or imply that Mayor Rahm Emanuel needed help. But it was the president's first direct comment on the issue since a stinging report from the U.S. Department of Justice released Jan. 13 that found Chicago police routinely used excessive force and violated the civil rights of citizens, particularly in the mostly minority communities that are hardest hit by violence.