Listening in on the Russian ambassador is normal intelligence work. Anyone in the US calling the Russian embassy has to expect that the FBI is listening because that's part of their job.
I'm not sure if this kind of wiretap has to be approved by the FISA court or if it is covered by another law. But I have never heard of a spy claiming that their call to a foreign embassy was recorded via illegal wiretapping.
It’s the leak of the wire tapping that’s the problem.
No, theh law states that when a US citizen comes on the line with a Russian, then monitoring must stop in the absence of a required court order. Either that was illegally violated or a couprt order was obtained to spy on Flynn. In which case, who requested the court order and which judge granted the request?
We pneed names and Fed prison sentences.