Russia's poisoning of a former spy in Britain is part of a Kremlin strategy to divide the West by conducting covert operations and then fomenting doubt and disagreement over who's responsible, U.S. Defense Secretary Jim Mattis has said. It was part of a pattern seen in Russia's actions, Mattis said, starting in Ukraine in 2014, where he said Moscow sent armed men without insignias into Crimea and has provided fighters and weapons under cover to Ukrainian separatists. Mattis said Russia's subterfuge continued through covert efforts to influence the 2016 U.S. presidential election. "They take the insignia off soldiers' uniforms and...