Gallup ought to be ashamed of this display of dumbstupid.
It's their annual "Who's the Greatest President?" poll. See if anything jumps out at you here:
George W. Bush higher up than Thomas Jefferson? What this proved to me is that the results had a little bit to do with the quality of "greatness", but mostly it appears to contain presidents who Americans can name. In other words, it's not so much of a "greatness" poll, but a "name a president" poll. The results, therefore, are dubious at best. Certainly, many of the same names would appear. But how else would Bush rank higher than Jefferson? Because he's more recent.
Oh, and Gallup admitted to it:
This "greatest president" question is open-ended, meaning that respondents are asked to name a president off the top of their head. This type of measurement tends to increase the mention of recent presidents.
So it's not an accurate measure -- at all.