I predict it'll eventually come out that CNN & Warren were in cahoots and tried to manufacture a "hot mic" moment.
"I think you called me a liar on national tv". Who says it like that? Why say "on national tv"? It's so unnatural.
Anyways, I'm gonna get me a beer.
They had a camera crew following Warren long before she got into it with Bernie and had the entire thing on that camera. It seems unlikely that they had the same setup for all of the candidates as they milled around.
A tipoff seems likely to me, especially since CNN's questions were just exactly what Warren needed to make the confrontation mean something.