Ordinary people don't follow politics closely and don't know very well what's normal, what's unusual or alarming, what's in & out of bounds. They absorb these things via "social proof," by watching how leaders of their various tribes behave. They take cues.
No set of facts is going to communicate *for itself* that something's alarming, unusual, a break from the norm, cause for mobilization. The way that's communicated is when people see their leaders ACTING AS THOUGH those things are true.
So when Mueller comes along and describes obviously impeachable behavior, your average lefty looks to the media & to Dem leaders to let them know whether & how it matters. And what do they find? A bland "both sides" smear in the media and Dem leaders nervously poll-watching.
Dems don't act like it's a four-alarm fire, so people absorb the message that it isn't one, and then they say that on polls, and then Dems point to the polls to say, "see? we're savvy! normal people don't care!"
Basically Dems seem to be in the grips of a lingering epistemological positivism that is rendering them politically impotent.
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