Clearly retaliation and abuse of power on McCabe’s part. How many other times has he pulled crap like this on other FBI employees and/or civilians? He’s shown a clear pattern of abuse of power: Special Agent Robin Gritz, General Mike Flynn, and his secret investigation on AG Sessions after his testimony to Congress. McCabe deliberately used the power of his position to intimidate, harass, and retaliate against people he didn’t like.
Obviously he found something useful on Sessions.