They refuse to believe what they see or hear. They only believe what he tells them to believe. I have never heard of anything as absurd as that. Have you?
"A high [right-wing authoritarian] can have all sorts of illogical, self-contradictory and widely refuted ideas rattling around in various boxes in his brain, and never notice it. . . .Research reveals that authoritarian followers drive through life under the influence of impaired thinking a lot more than most people do, exhibiting sloppy reasoning, highly compartmentalized beliefs, double standards, hypocrisy, self-blindness, a profound ethnocentrism, and — to top it all off — a ferocious dogmatism that makes it unlikely anyone could ever change their minds with evidence or logic."
(From sociologist Bob Altemeyer's book The Authoritarians, via Glenn Greenwald)
Thus, when one of TEH STOOPID EBIL LIBRUHLZ lies, it's an indictment of all STOOPID EBIL LIBRUHLZ and an indication of their moral bankruptcy.
When Der Pumpkinfuhrer lies (which he does A LOT), well...it's just an exaggeration in service of The Just Cause.