No need for manipulation; cutting is enough. The turning point for me from "doubt, but verify" to "default to believing it's an outright lie" was the infamous fish feeding video[0].
If manipulation becomes commonplace, more people will default to "doubt", which is good.
I’ve seen it on TV since I was a kid with “reality” tv shows, and I have never have understood the psyche of people that like to watch fiction under non fiction pretenses. People like being fooled I guess.
I think intransparent processes/businesses are to blame for a lot of reasonable doubt concerning all kinds of things, which is then used by actors with an agenda to influence what people can read from the noise.
I think the way to neutralize information warfare (an incredible flood of cherry picked 'takes') is to have businesses and politics become more transparent, to a degree that would seem extreme (and individuals more anonymous).
If manipulation becomes commonplace, more people will default to "doubt", which is good.
[0] https://www.snopes.com/fact-check/did-trump-impatiently-dump...