Updates:

July 1, 2008: Added former Bush administration official Rob Portman.
July 2, 2008: Added retired Marine Gen. Anthony Zinni and Rep. Chet Edwards, D-Texas. Made Sen. Chuck Hagel, R-Neb., available for both Obama and McCain.
July 3, 2008: Added former Maryland Lt. Gov. Michael Steele; Rep. Mike Pence, R-Ind.; and Gen. David Petraeus. Removed Sen. Mel Martinez, R-Fla., and Rep. Ileana Ros-Lehtinen, R-Fla., who were both born in Cuba.
July 9, 2008: Added Rep. Eric Cantor, R-Va., and reader comments to some profiles.

Slate intern Tony Romm contributed to this feature. Interactive components by Chris Wilson, and design by Jim Festante.