U.S. Attorney General Richard Olney and President Grover Cleveland justified federal intervention in the Pullman strike of 1894 on the grounds that
A) the union's leader, Eugene V. Debs, was a socialist.
B) the strike against the railroads was crippling all parts of the American economy.
C) the strikers were engaging in violent attacks on railroad property.
D) shutting down the railroads threatened American national security.
E) the strike was preventing the transit of U.S. mail.