It is a diabolical bit of black magic, but history sadly tells us it sometimes works.
First, the demagogue destroys trust in everything and everybody. When it comes to trust, this creates—as strange as it seems—a level playing field. That is, if you can’t trust everyone, you might as well trust anyone.
Second, the demagogue says: If you might as well trust anyone, why not me? I’m no less trustworthy than anybody else.
A logician can blow holes a mile wide in this, but people are not logicians, they are people. People “think” with their feelings (it is common for Trump to reach conclusions about what he “feels” where others would usually offer thoughtful support).
Where suffering could be alleviated by thinking and truth, demagogues offer feelings and lies. Where chaos is self-inflicted, demagogues offer promises of order. Where trust is eliminated, demagogues say “trust me.”