Flynn told the Russian ambassador to work with the Trump transition team against the Obama administration: don’t let them “box us in.” Apart from telegraphing Trump’s eagerness to get on with Putin, this also gave the Russians something to use against Flynn later on.
Put another way, the forthcoming NSA had asked a foreign official to help mitigate or undermine U.S. policy. You don’t really need a secret decoder ring to see why this alarmed the FBI.
Flynn then lied about the content of this call and got the VP to do likewise. As Mueller found: “The public statements of incoming Administration officials denying that Flynn and Kislyak had discussed sanctions alarmed senior DOJ officials...”
“... who were aware that the statements were not true.” Moscow was also aware the statements were not true and there’s a good chance they had their own recording of this call about helping the Trump team outflank the Obama admin.
No doubt Flynn’s defenders will argue he was trying to lessen Russia’s retaliation and that’s a good thing. But from a CI perspective, the gravamen was Flynn enlisting Kislyak/Moscow’s help to undercut the acting POTUS.
... And what the Russians might do with that information in future.
