Special Counsel Robert Mueller’s Russia probe is over, but the FBI is almost certain to continue its counterintelligence investigation into Russian espionage efforts related to the 2016 election. The FBI will continue to search for Americans working on behalf of the Kremlin. John Sipher writes in The Atlantic that the inability to establish that the Trump campaign conspired in a “tacit or express” agreement with the Russian government is not surprising. Most espionage investigations come up empty unless and until they get a lucky break. That does not mean there was no espionage activity in relation to the 2016 election. Every previous Russian political-warfare campaign was built on human spies. Russian “active measures”—propaganda, information warfare, cyberattacks, disinformation, use of forgeries, spreading conspiracies and rumors, funding extremist groups and deception operations—rely on human actors to support and inform their success. Counterintelligence professionals must doubt that Russia could have pulled off its election-interference effort without the support of spies burrowed into U.S. society or institutions.