Senators with low approval ratings

According to SurveyUSA there are some Senators who have approval ratings that are quite low, many of whom are somewhat unexpected. Here are the Senators who have approval ratings that are either more negative than positive or that are quite close

Jim Webb (D-Virginia): 42 approve, 47 disapprove
John Cornyn (R-Texas): 44 approve, 42 disapprove
Jim Bunning (R-Kentucky): 40 approve, 48 disapprove
John Kerry (D-Massachusetts): 40 approve, 53 disapprove

There are also others who are not doing so well, such as Frank Lautenberg (D-New Jersey) but its too early to figure out what's going to happen 6, 4, or even 2 years from now. Still, some of these are surprising.