Nate Silver: And since we're on the subject...

Nate from the same article as before:

The thing is, though, that Obama's approval rating haven fallen to 50 percent is not particularly newsworthy. There's no reason that a drop from 51 percent to 50 percent, or from 50 percent to 49 percent, means anything particularly more than a drop from 58 percent to 57 percent, or from 37 percent to 36 percent.

First of all, although I'm on record as being quite pessimistic about what's liable to happen to the Democrats in 2010, odds are that Obama's approval will have to be somewhat worse than 50 percent for the Democrats to lose the House. The relationship between Presidential approval and his party's fate at the midterm elections is quite linear. An approval rating of 50 percent would typically be associated with a loss of about 26 seats:

The Democrats, however, currently have a 78-seat advantage in the House, meaning that it would take a 39-seat loss for them to lose control of the chamber. The over-under for how unpopular Obama would have to be in order to be more likely than not to cost his party those seats is not 50 percent -- it's probably more like 42 percent. Now, certainly, there's some margin for uncertainty there: Dwight Eisenhower's Republicans, in '58, lost nearly 50 seats even though his approval was in the high 50's. But the point is, there's nothing particularly magical about Obama being above or below 50.

Likewise, Obama can probably afford an approval rating below 50 percent and still be a favorite to win re-election in 2012. George W. Bush won in 2004 with an approval rating of 48 percent, and Harry Truman won in what was considered a huge upset in 1948 with an approval number that had last been tested at 39 percent, although that poll was several months old at the time of the election.