An outstanding analytical piece on this years upcoming midterm Congressional elections by Jay Cost courtesy of OpinionJournal.
Cost shreds the conventional wisdom that the House will go Donkey and the Senate will stay with the GOP. He bases his observations on 46 observations (92 years) during which the House has never switched parties without the House also doing so. This is more than statistical anomaly - Cost cites some very compelling reasons. Among them, Senators, due to higher profile, inability to redraw districts and the likelihood of better organized opposition are much more vulnerable than their House counterparts.
Read it - it's well worth your time. This doesn't mean though that Ken Mehlman can rest of his laurels.