He had NO EXPECTATION of being spied on for talking to a Russian Ambassador.
He most certainly did. Anyone talking to a Russian official in this country is going to be surveyed. And if overseas, that country's intel service will be surveying both and, if it's an ally, will share that intel with the CIA.
The Russian Ambassador was invited by the OBAMA state Dept to BOTH conventions. It's a tradition. The guy is on the "A list" for parties and get togethers. It is NOT suspicious to meet with him or talk to him. And CERTAINLY, there are AMPLE opportunities to do so. As I said, any one with Flynn's Intel background would know HOW to avoid surveillance if anything nefarious or illegal was to happen.
This is not the only time they communicated. Plus, Michael Flynn spoke with him 5 times Christmas week.
Obviously, the FBI has other instances that you and I are not privy to. Hence, the "more than circumstantial evidence" statements.
Anything intercepted on a FOREIGN collection (covers foreign embassy personnel in USA) cannot be directly tapped or used for DOMESTIC surveillance without a separate FISA declaration. And UNMASKING any US citizens requires even further review and approval. Flynn was NOT a security threat. He was vetted and probed more than a female Kardashian. Therefore GETTING approval to unmask him and REVEAL a fairly innocuous, benign conversation was CLEARLY illegal.
HOWEVER -- You don't NEED separate authorization to pick up that same conversation under the collections and recording of our "terrorist" PATRIOT Act Domestic spying system. It's already there. And that's likely where the info was leaked from.
I have a GUESS about why Flynn MADE that contact in the 1st place -- but you are not the people to discuss that with...
Blah, blah, blah.
You don't know that they know. You're guessing. You have absolutely no clue as to what other evidence the FBI, or the intel service of a friendly country, catches in their nets.
Consider other Russians, other foreigners speaking amongst themselves about all this, and we listening much in the way that we were able to eavesdrop on "chatter" to find al Qaeda. What, did you think we only employ those tools against Arabs?