When you get all your news from social media, and you and your friends think a candidate "tells it like it is," but there is contradictory evidence, you and your friends will tend to reject that evidence.
More generally, when your Bayesian prior belief in a candidate gets too high, anyone who disagrees just makes themselves seem disreputable in your eyes; their disagreement strengthens your belief in the candidate.
What could count as direct evidence that the candidate is wrong, when you and your friends have filtered all of your news?
Most people don't actually get their news from social media.
The people who do spend an inordinate amount of focus social media, and who've gone lurching off into a little bubble, are the journalists. They've spent the last year being shocked that the public keeps disagreeing with them and their circle of friends. Surely tomorrow the public will see how stupid it is to vote for that nasty Mr Trump that Twitter keeps condemning and that Mr Rubio is the only nice shiny acceptable candidate. No? Oh well, next week then. Still not, goodness why can't these people get with the Twitter vibe. Surely next month then...
Sanders and Trump are quite different. Sanders has picked up votes from the social bubble moving leftwards into his territory. Trump has picked up votes from the people outside the bubble staring in incredulity as the bubble gets more inward looking and spends more and more of its time raging about what candidates can and cannot say. (Which is why every controversy helps Trump -- he's essentially made rebellion against that his campaign... the candidate who will not be cowed)
With the exception of Sanders (whose propositions do not make fiscal sense) all of the candidates, are unbelievable or have had a history of being unbelievable. So, it's not as if there is one [viable candidate]* who is immune to lies, exaggerations, distortions, obfuscation, scandal etc.
Kasich and Carson [and O'Malley?] are "too nice" to win anything.
More generally, when your Bayesian prior belief in a candidate gets too high, anyone who disagrees just makes themselves seem disreputable in your eyes; their disagreement strengthens your belief in the candidate.
What could count as direct evidence that the candidate is wrong, when you and your friends have filtered all of your news?