In the wake of President Obama's speech to the nation about BP and the Gulf last night, it's worth noting that his approval ratings have not been affected by the spill so far. The speech is unlikely to have a significant effect either.
I'm laying down a marker on these two points because of the likelihood that a post hoc narrative will be created in which the Gulf spill and/or the speech played a major role in Democratic losses in the 2010 midterms or a subsequent Obama defeat in 2012. This is precisely what happened after Jimmy Carter's so-called "malaise" speech, which is frequently used to "explain" Carter's subsequent defeat in 1980. Here, for example, is a random Omaha World Herald editorial from 1995 I found in Nexis:
A few commentators seized on Clinton's rumination and compared it to Jimmy Carter's 1979 "malaise" speech. Carter's call for America to shake itself out of a national malaise and regain its self-confidence was perceived by some people as a whiny effort by a president searching for something to blame for his low ratings in the polls. It's believed that in appearing to rebuke the public, Carter alienated voters, contributing to his election defeat in 1980.
In reality, Carter's approval ratings after the speech, while low, were generally stable until the Iranian hostage crisis. His defeat can easily be explained by the state of the economy, which was terrible:
Remember, dramatizing an event (e.g., Carter's defeat) is not the same thing as explaining it. It's not clear that the malaise speech had a significant effect on Carter's fortunes, and so far there's no evidence that the oil spill or last night's speech have had a significant effect on Obama's.
Update 6/17 3:49 PM: See also Greg Marx's take at CJR.