Counterintelligence is, in effect, chasing ghosts, which is why the tools used to investigate foreign intelligence activity are secret, like human sources or electronic surveillance.

As a former FBI counterintelligence agent who investigated foreign propaganda cases, I’ve seen firsthand how foreign intelligence services leverage American freedoms - and the constitutional limitations on the FBI’s investigative power - to their advantage."

Exposing the activities of a foreign intelligence service renders them ineffective, since it removes plausible deniability, which is the hallmark of covert intelligence operations.

In the case of someone sharing classified information with foreign intelligence, for example, the FBI could surreptitiously ensure that they are no longer able to obtain sensitive information.