No, I think Papadop was a complete surprise to them--he blabbed to Australian intelligence while drunk and that's how they got them because he'd been talking to one of the other four. And I think Sessions just thought he could climb the ladder to do some racism, and had no idea that Russians were truly involved until he was talking to the other four.

I think it's Flynn and Manafort for sure. And likely Stone and Carter Page for the other two, but Trump himself or Trump Jr. could be one of those four. But from what's publicly known, Flynn, Manafort, and Page were all under surveillance before Trump hired them for his campaign, or for his staff.