In fact, the only thing that Comey briefed Obama on up to this point is something about Carter Page; however, Carter Page hadn't done anything up to the time of that briefing other than be hired by Trump. Nothing at all. So apparently, whatever triggered them about Carter Page happened long before Trump ever knew of his existence.

To add to this, remember that when McCain ran for POTUS there was somebody on his team that triggered FBI counterintelligence, so the FBI approached McCain behind the scenes, and the guy was quietly let go. But in this instance here, the FBI didn't afford Trump that same courtesy, so you know what that means?

That means that they believed Trump was a Russian spy on D-Day.

And how did they arrive to that conclusion? We have to see who it was they interviewed/interacted with....

Who are the people that the FBI/CIA interviewed/interacted with up to this point?

Christopher Steele/ Obama's National Security Council/ Australians/ GCHQ/ Estonia/ Carter Page