This business of Travis Childers winning an extremely Republican district on the heels of two other Democratic special election wins drives home how infuriating the idea of even having an extended "electability" argument about "who can win" is at this point. The reality is that given current conditions, either Clinton or Obama is very likely to win. That, I assume, is why Clinton is fighting so hard. There's no need to join David Corn in reaching for esoteric explanations, she's fighting hard for the prize of the nomination because it's a very good prize to have.
Objective conditions could, of course, change. Maybe some kind of spate of unexpected good news from Iraq or the economic picture will save John McCain. But unless that happens, he's looking to be in terrible shape. The GOP brand is so terrible that it's dragging candidates down in solid red districts, and McCain is currently doing not-so-hot in polling matchups even though Americans are now inundated in unflattering information about Clinton and Obama while most people have never heard sustained from-the-left criticism of McCain.
On the House side, NRCC chair Tom Coles seems to be heavily leaning on the notion that it's somehow underhanded of Democrats to nominate culturally conservative candidates to run in culturally conservative districts. Needless to say, the GOP does the same thing in culturally liberal districts because this is just common sense. But more to the point, the idea that the GOP can turn the ship around by November by "revealing" this strategy is going to be of little comfort to the large number of Republicans defending more culturally moderate districts outside of the South. Democrats aren't going to pick up many more seats in places like the MS-1 but they hardly need to.