So how come people trust Donald Trump? How is it that he can get away with lying whenever he opens his mouth, how is it that people buy it when he pretends he's the underdog and not part of the establishment? How is it his followers, who are so ready to believe that the government lies to them all the time, don't call anything of what he says into question?

If we go by what you say then we're basically fucked. Government and authorities can never regain trust because thanks to people like Trump, thanks to parties like the Republicans, who have spent decades undermining that trust, thanks to the mass media who are highly complicit, we live in a post-truth world, and it's enough that a government wasn't 100% truthful that one time, we can never trust them again.