The campaign was under investigation since July.
The Ambassador is routinely surveilled without relation to that.
They pick up Flynn on one of those calls. That info is passed on to the investigators.
The leak of Flynn's name? How is it any different than the FBI leaks of the Weiner computer and the false FBI leak to Bret Baer that the Clinton Foundation was going to be imminently indicted? You had no problem with those leaks as I recall.