Secretary of State Antony J. Blinken warned on Monday that a malicious “flood” of disinformation was threatening the world’s democracies, fueled in part by the swift rise of artificial intelligence, which he says sows “suspicion, cynicism and instability” around the globe.Mr. Blinken spoke in Seoul at the Summit for Democracy, a global gathering organized by the Biden administration, which has made countering the authoritarian models of nations like Russia and China a top priority.Mr. Blinken, who as a young man worked briefly as a journalist, said that changes to the…