Everyone is a whole lot more susceptible to propaganda than anyone admits. Doctorow presents this as Klansman getting the message that Trump is their guy. Mao, Goebbels and any other obvious-baddies are perfect for making the point. By pretending like it doesn't happen TO YOU, you'll accept that it can possibly happen to humans (that are not you).
But it happens to everybody, all the time.
The only propaganda we notice is the stuff that is so far from targeting us we see it's comically incongruity. But propaganda isn't meant for the hard sell. Propaganda doesn't change your mind. Propaganda gets you to cross the threshold and do something you were already positioned to do, by giving you meaning for doing it.