The mole: Stefan Halper, a Cambridge professor.
Supposedly, Halper was gathering information for the FBI about a suspected Trump-Russia connection.
Well, what else has Halper done? At The Intercept, Glenn Greenwald reports: "Four decades ago, Halper was responsible for a long-forgotten spying scandal involving the 1980 election, in which the Reagan campaign – using CIA officials managed by Halper, reportedly under the direction of former CIA Director and then-Vice-Presidential candidate George H.W. Bush – got caught running a spying operation from inside the Carter administration. The plot involved CIA operatives passing classified information about Carter's foreign policy to Reagan campaign officials in order to ensure the Reagan campaign knew of any foreign policy decisions that Carter was considering."
Oops. That doesn't smell good. CIA operatives, managed by Halper, infiltrated the presidential campaign, spied on Jimmy Carter and his advisors, and relayed information about Carter's foreign policy to Reagan's team.