Hyman and Sheatsley in 1947 wrote about "chronic know-nothings," a hardcore group of people completely disconnected and largely unreachable by traditional information campaigns. "Even if all the physical barriers to communication were removed," they wrote, "there would remain many psychological barriers to the free flow of ideas."
These are people with no motivation and often little ability to participate in the public discourse. Basically these are people who don't give a damn about public affairs and see no reason why they should. There is a certain Downsian rational beauty to this: why should I bother keeping up on something I have no real voice in? What benefit do I receive by spending time or money in keeping up with public affairs?
Other than civic responsibility, something that sure as hell won't work on them, there's no good answer.
Who are the chronic know-nothings? No real surprises here. The Pew data suggests they are younger and less educated, women more than men, non-white and lower income, and more likely to live in the South than elsewhere. Other studies confirm this. What people know is often tied to various demographic factors, though if you control for one or two of them the other factors often disappear in importance.
Analyses I would love to do some time is whether this hardcore group of chronic know-nothings is growing (probably yes) and whether the demographics are shifting (I suspect so) and are there also changes in voting habits (maybe yes) and where the media fit in all this (little, if any) and whether this group is more open to persuasion (absolutely).