But who determines the truth? Politicians, Historians, Clergy, Journalists, etc?

You are falling into the trap of thinking there are 'competing' truths, or 'alternate' facts. This enables liars to say 'oh, that's just your truth,' denying the power of truth to show them wrong.

There is only one truth, and it is true by itself, no one 'determines' it. The persons you name may tell the truth, or they may not. It's important to expect that they will, and hold them to account if they do not.

Lesson Eleven from Historian Tim Snyder:

Don't assume--get to know people. All sorts of people. Ignorance is never strength.

And, I think part of what Snyder is saying here is good relations with those around you is a defense against being a 'other' who can become a target for gossip and denunciation if the times become 'McCarthy-like.'

Well stated

Lesson Twelve from Historian Tim Snyder

Don't let the haters feel like they have claimed the territory.

Lesson Thirteen from Historian Tim Snyder

And participate in campaigns. And consider running for office.

Problem with that is everyone but republicans are expected to be pure as the driven snow and fully vetted. Republicans can be liars, crooks and con men and they will always be handily elected. Mainly because of the ignorance of the average republican voter and gerrymandering.

It's really hard to fight stupid.

If it were easy, we'd have a lot fewer problems.

Lesson Fourteen from Historian Tim Snyder

This goes with the ones about keeping countervailing institutions alive.

I'm a sustaining member at NPR, a counter to "alternative" facts.