What's the big deal about presidential approval? So what if Bush is at 36 (NY Times/CBS) or 42 (Gallup and CNN) or whatever?
"There is, however, a historical correlation between presidential approval ratings and midterm Congressional election results (at least at the House level). This site compiles historical presidential approval ratings dating back to 1937, when Gallup first started doing the poll."
While not predicting a 40 seat drop for R's this year (the landscape is different with redistricting and the professional marketing of the GOP vs the amateur Dems), the graph clearly shows the historical precedent for low approval correlating with loss of House seats in a midterm.
Don't be fooled by a claim of 42% being a rebound for Bush. These are historically low levels of approval even if they're not outliers. Speaking of Prof. Franklin (previous link), he also summarizes the historical data at Political Arithmetik from a post dated 11/05.
For example, compare the decline prior to the 1992 elections in President George H. W. Bush's approval with those of President George W. Bush. The elder Bush is a clear example of "free fall", the sharpest and largest approval drop since President Nixon's in 1973-74. President George W. Bush's decline more closely resembles the long-term decline of Jimmy Carter's approval than it does the free fall of either the elder President Bush or President Nixon.
People have made up their mind about Bush. What he now has is a thick ceiling and a thin floor in the polls. Dems will never trust him again, and indies have their doubts. Republicans will hug him like a life preserver, which won't stop them from abandoning him if it looks like they might drown.