The Justice Department dropped charges Thursday against a Massachusetts Institute of Technology professor accused of concealing ties to the Chinese government, a further setback to a federal initiative that was set up to prevent economic espionage and theft by Beijing of trade secrets and academic research. The department revealed its decision in the case against Gang Chen in a filing in federal court in Boston, saying it could no longer meet its burden of proof. U.S. Attorney Rachael Rollins, the top federal prosecutor in Massachusetts, said the move was “in the interests of justice” and was the result of new...