Here’s a little context. Let’s take a journey back to the early days of 2006. At this stage in the game, Clinton held a commanding lead over her Democratic opponents, with CNN/USA Today’s polling at the time showing her with 39 percent of the Democratic primary vote. She was trailed distantly by John Kerry at 15 percent, Al Gore at 13 percent, and John Edwards at 12 percent. Mark Warner and Joe Biden each garnered 5 percent. Of those, of course, only two would actually go on to challenge Hillary for the nomination, with one winding up a laughingstock and the other winding up as vice president.
Barack Obama was not even an option. In fact, CNN’s polling did not add him to their list of choices for president until October of that year, after his announcement that he would be exploring a bid (PDF).
Or let’s consider the complete insanity of the polling of the 2012 Republican field, where everybody (besides, I suppose, Jon Huntsman) got their moment at the front of the pack, even as the primaries themselves were unfolding. While Mitt Romney was very slightly ahead in early 2010, roughly a thousand days out from Election Day, polls at that point still included many names of those who wouldn’t ultimately run, and missed many names of those who would. (PDF)