At FiveThirtyEight today, Nate Silver unveils the mysteries of the Gallup Tracking poll cross-tabs, and provides a fascinating comparison of Barack Obama's recent standing in various demographic categories to John Kerry's 2004 performance (as measured by exit polls).

Turns out Obama's doing better than Kerry in every category other than one: self-identified Democrats, where he trails Kerry by nine percentage points. Obama, on the other hand, beats Kerry among self-identified Republicans by fourteen percentage points.

Aside from issues related to the changing partisan composition of the electorate since 2004 (a sizable drop in GOP identification, with modest gains for Democrats and a big increase in indies), this particular finding should be regarded as transitional, since the dynamics of a general election campaign will almost certainly boost Obama among Democrats and McCain among Republicans. But it's still interesting.

The most impressive Kerry-to-Obama gains are among Hispanics (up 28%, though exit poll underestimation of Kerry's Hispanic percentages is a factor there), and voters under 30 (up 21%).