This National Journal map doesn't strike me as a particularly useful guide for the GOP's chances of taking back the House. It obsesses over which Democrats represent districts that voted for President Bush in 2004. But 2004 was, you know, four years ago. This year Barack Obama clobbered McCain in every Kerry state and all of the non-deep South, non-Great Plains, non-Arizona Bush states. As a result, outside the deep South, basically every Democrat is from a "safer" district now.
Look at Virginia. The first number is how much of the vote John McCain scored in this district. The second number is what George W. Bush scored four years ago, when he easily defeated John Kerry statewide. I've bolded the districts where the representative is now from the party whose presidential candidate lost the district. (VA-02, VA-05, and VA-11 all replaced Republicans with Democrats this year.)
VA-01: Rob Wittman (R) - 51% (60%)
VA-02: Glenn Nye (D) - 49% (58%)
VA-03: Bobby Scott (D) - 24% (33%)
VA-04: Randy Forbes (R) - 49% (57%)
VA-05: Tom Perriello (D) - 51% (56%)
VA-06: Bob Goodlatte (R) - 57% (63%)
VA-07: Eric Cantor (R) - 53% (61%)
VA-08: Jim Moran (D) - 30% (35%)
VA-09: Rick Boucher (D) - 59% (59%)
VA-10: Frank Wolf (R) - 46% (55%)
VA-11: Gerry Connelly (D) - 42% (50%)
See what happened? Only two of the state's six Democrats are in McCain-voting districts, one of them in a squeaker (Perriello) and one whose southwest district is so safe for him that the GOP didn't even field a challenger (Boucher.) Two of the state's five Republicans are now in Obama-voting districts, even though their districts voted for Bush last time. And two of the three Democrats elected this year, Connelly and Nye, are in districts that swung from Bush to Obama.
Keep in mind, all of this happened in a state whose Republican governor and legislature started the decade by gerrymandering the districts for maximum GOP strength. Bush carried nine of Virginia's 11 districts twice. McCain carried only five of them. Once we learn the full results from states like Michigan, Minnesota, Indiana, Iowa and Wisconsin, places where Obama dramatically outperformed in the suburbs, I think we'll learn that most congressional districts went blue at the presidential level. In 2004, 255 congressional districts had gone red.