Sen. Charles Schumer, D-N.Y., gestures as he speaks to family and friends of victims of gun violence, on Capitol Hill in Washington, Wednesday, Nov. 13, 2013, during a news conference marking the 20th anniversary of the passing of the Brady Bill. CREDIT: AP Photo/Charles Dharapak A quintet of Senate Democrats is asking the Centers for Disease Control and Prevention (CDC) to provide an update about its gun violence research in a letter sent to the agency.