> R's perceive (sometimes not incorrectly) that lying is a "both sides" thing

Lying is a politician thing. Anyone who thinks that any one politician or political party has a monopoly on lying is deluding themselves. Trump lies through his teeth, Biden lies through his teeth, Obama did, Bush did, Clinton did, etc. Honest politicians simply do not exist.

And to be clear I think we should absolutely criticize our politicians for it. What I object to is this framing like only one particular politician is a liar. Bullshit, they all are liars to the same degree.