WASHINGTON — The Justice Department is launching an effort in five cities in the U.S. to reduce spiking gun violence by addressing illegal trafficking and prosecuting offenses that help put guns in the hands of criminals.Attorney General Merrick Garland will launch the gun trafficking strike forces in Chicago, New York, Los Angeles, San Francisco and Washington, D.C. The effort will include stepped-up enforcement in so-called supply areas — cities and states where it’s easier to obtain firearms that are later trafficked …