The Washington Post writes tonight that the Trump transition team did warn Flynn over his Russian meetings. This looks like a piece to cover the Trump team's ass.
But the head of the transition team was Mike Pence, who claimed publicly not to have known about Flynn's dealings with the Russians or the fact a Russian paid for Flynn's lobbying on Turkey's behalf. Flynn was fired a couple of weeks after Sally Yates warned the Trump White House that flynn was vulnerable to blackmail from the Russians.
The question then is why it took the Trump White House so long to fire Flynn and what did Pence really know.