a) there is no FBI investigation-- routine eavesdropping intercepted Flynn talking to the Russian ambassador;
b) all incoming NSA's talk to the Great Powers;
c) the media is lying about a purported investigation;
d) Flynn may have misspoken, but did not deliberately misinform anyone;
e) Flynn has my full confidence and will remain as NSA
Trump didn't do this, so I suspect there's more to it. My guess is (d) is incorrect-- Flynn misled them about something.
I think so too, but again, that’s speculation. We don’t know. As is, the best case is to hope he goes away and is gone.