Erosion of Trust - might be the most accurate and honest reason for Flynn's departure.
Trust- NOT over what he may or may not have discussed with the 'Russians'. Those discussions were perfectly legal and normal for any and ALL incoming administrations.
The problem was the 'inaccurate information' given to the Vice President.
There are only 3 possible explanations for this, as I see it:
1. Flynn lied.
2. The VP and Admin lied about what Flynn told them.
3. Flynn honestly didn't recall exactly what was discussed.
Obviously,
#1 - Immediately gone - not acceptable.
#2. The Admin put themselves in a lose-lose situation, leaving a hard choice - back a good man, and let the situation fester, which would only get worse, or have the problem go away with Flynn's resignation - ie. a scapegoat.
#3. This would be the most concerning - because IF Flynn really didn't recall exactly what he discussed with the second/third most powerful nation in the World - then he was not as well qualified for the post he held as he should have been.
I consider #2 and #3 reasons to be most likely.
What is MOST concerning, however is the leaking that continues like a floodgate. Mark Levin suspects Preibus of these leaks - I suspect the DOJ - especially given the actions of the prev. 'temporary' AG whatshername and her involvement with the Flynn affair, especially in light of her disloyalty over the Immigration Ban business. SHE could definitely have leaked the Flynn info about the phone call - or any one of numerous rotting corpses that still occupy the DOJ.
In any case -it is time for the NEW AG, Jeff Sessions,to TOTALLY clean house at the DOJ - fire ALL the previous admin lawyers (just as Ø did when he came in.) We HAVE TO HAVE a DOJ that can be TRUSTED. Right now, we do not.