Through a combination of stories that came out yesterday, it seems pretty clear to me that Michael Flynn directly aided ISIS while acting as a foreign agent for Turkey.
The Miami Herald reports that it was Flynn who told the Obama administration at the very end of his term not to work with Syrian Kurds to retake the de facto capital of ISIS in Raqqa. The reason the Obama administration asked the Trump transition is because the operation would start after the inauguration. Turkey considers all Kurds to be terrorists or at least enemies of their state so to have an agent of Turkey sideline the Syrian Kurds is hardly surprising. The treason part comes in that this delay in attacking Raqqa could be considered material aid to an enemy of the United States. Regardless though Flynn was clearly acting against the interests of the United States for his own personal profit.
To make it worse
The New York Times reported that Flynn knew he was under investigation by the FBI for his foreign connections and told the Trump transition team about it on January 4th. Well before the Trump team has said it knew. The person who headed the transition was the Vice President. This puts Pence in the very awkward position of having lied multiple times about when he knew Flynn was compromised.
We also know now that after Flynn was forced to resign that Trump tried to get the FBI to "let this go" which would appear imply that Trump knew about all of this the entire time despite him saying he only found out from news reports.
Combined all of this makes it look like both the President and Vice President were at best tolerant of letting Flynn influence American foreign policy for profit, or worse complicit it acting against American interests.