At its most basic level, Hillary Clinton’s polling problem is pretty simple: Everybody knows her.

When a poll reveals that, say, 20 percent of voters have a favorable impression of Candidate A, and 30 percent have an unfavorable impression, and 50 percent don’t know enough to have any impression — well, it’s not great news, but it also says Candidate A has room to grow. He or she can work on that big group of undecideds and try to leave them with a favorable impression.