"For every complex problem there is an answer that is clear, simple, and wrong."

The issue is that the stupider the politician, the more likely they are unable to understand why their clear, simple answer to the ills of the world is also wrong.

Brexit, whatever is happening in the US, is caused by narcissism (a common trait among politicians) paired with a great deal of stupidity and ineptitude, not only among politicians, but among the populace as well.