I think you are right in truth itself is not really knowable in many interesting cases — but I think we already would be okay with a level lower: what if we manage to get rid of verifiable untruths?

You know the "X says Y is true and Y can be objectively checked because there is a definition for what Y is". I think that the US had a corrosive atmosphere even before Trump already, think about the whole "candidate X is socialist/fascist". Not to take a political stance, but there are definitions for those terms and checking if something is untrue is just a matter if the reality of what candidate X says or does fits that definition.

This is what media was supposed to do and this is what public discourse was meant to be before parties became tribes, before the footballification of politics.

Media has no incentive to do this nowadays, as they have to fight about your brain time with much nicer and more exciting media products.