As far as I can tell, knowing explicitly whether somebody's political leanings were shifted is an impossible metric to test—earlier, now, or later. People are p

As far as I can tell, knowing explicitly whether somebody's political leanings were shifted is an impossible metric to test—earlier, now, or later. People are prone to lying about those things (either to themselves or to others for many reasons). If you want to see one (non-scientific) example of media affecting someone's political outlook, I recommend https://en.wikipedia.org/wiki/The_Brainwashing_of_My_Dad https://en.wikipedia.org/wiki/The_Brainwashing_of_My_Dad It's from before all of this and mainly focuses on Fox News'/talk radio style of vitriolic, non-factual reporting. Similar tactics were employed and amplified. I'd be surprised if they had no effect with the amount of noise that has gone up. I've personally seen it in others as well, but I understand that adds little to your search.