The United States should threaten to retaliate if Russia does not stop attacking U.S. assets in Syria, former national security adviser Zbigniew Brzezinski wrote in a Financial Times op-ed published Sunday, urging "strategic boldness," with American credibility in the Middle East and the region itself at stake. Moscow's apparent decision to strike non-Islamic State targets and those of Syrian rebels backed by the Central Intelligence Agency "at best" reflects "Russian military incompetence," and worst, "evidence of a dangerous desire to highlight American political impotence," wrote Brzezinski, the national security adviser for former President Jimmy Carter and a strong supporter of...