The events surrounding the FBI’s NorthernNight investigation follow a pattern that repeated for years as the Russian threat was building: U.S. intelligence and law enforcement agencies saw some warning signs of Russian meddling in Europe and later in the United States but never fully grasped the breadth of the Kremlin’s ambitions. Top U.S. policymakers didn’t appreciate the dangers, then scrambled to draw up options to fight back. In the end, big plans died of internal disagreement, a fear of making matters worse or a misguided belief in the resilience of American society and its democratic institutions.

One previously unreported order — a sweeping presidential finding to combat global cyberthreats — prompted U.S. spy agencies to plan a half-dozen specific operations to counter the Russian threat. But one year after those instructions were given, the Trump White House remains divided over whether to act, intelligence officials said.