Oddly, I recall an America where testimony like that was routinely impeached since the witness is clearly being coerced.
That's what I would think. Anything Manafort says now is said under duress. It would have to be corroborated by others, who aren't under duress.
Not that there is anything to say. They can't even seem to find any Russian interference in the election, that's not simply free speech. And if there was no Russian intererence, there couldn't have been collusion.
Perhaps that is a part of our distant history.