People already have trouble telling propaganda from fact. That has been going on since forever.
At the end of the day I don't see this being a game changer. If anything, now video and photos are less evidence for/against something as the potential falseness becomes well known. Congressman X: "no, that wasn't me you saw leaving the hotel with the prostitute, my slimy opponent obviously is deep faking stuff".
And people will continue to believe what they want to believe, in spite of all evidence to the contrary, just like they do right now.