Matt Glassman explains the difference between Know-Nothings and Knowing Nothing in American politics:

 I’ve detected a rise in the use of the term as a blanket charge of anti-intellectualism. There’s certainly nothing wrong with that — the meaning of words and phrases change all the time. But it’s interesting to see the process occur in real-time, and watch how a historical word slowly drifts from one meaning (the name of a party) to another (a slur based on that party’s positions) to another (a general slur based on the plain meaning, but incorrect, assessment of the party’s name).