Arrr... Tim Storey be stealin' me thunder. Over at Sabato's Crystal Ball, Storey suggests some ominous signs for Democrats who are trying to hold onto state legislatures across the country this fall. He produces a nice graph (below), going back much further than I did, basically showing that the president's party never gains state legislative seats in midterm elections.* The only two exceptions were 1934 (huge economic growth in the middle of the Depression) and 2002 (following the 9/11 boost for Bush and Republicans).
*For some reason, using Klarner's data, I find that Democrats gained 10 state legislative seats in 1998, while Storey finds them losing a handful. Can anyone explain this discrepancy?