Tom Jensen, of Democratic Public Policy Polling, writes:

It may be the Midwest — rather than the South — that proves to be the worst region for Democrats at the polls this year. We’ve polled on Barack Obama’s approval rating in 16 states since the beginning of March. In 6 of those his approval rating is 10 points or worse than the share of the vote he got on election day — and all but one of them is a Big Ten state.

Obama’s approval in California on our last poll represented a 12 point drop from his 2008 performance. The other five ones are all Midwestern — Illinois (50% approval, 62% 2008 vote), Ohio (40% approval, 51% 2008 vote), Michigan (46% approval, 57% 2008 vote), Iowa (43% approval, 54% 2008 vote) and Wisconsin (46% approval, 56% 2008 vote).

As Jensen notes, this could put at risk five Democratic governors in each of these states. But it also may help the GOP nail down Midwest Senate races. Rasmussen reports that Dan Coats leads in Indiana by 14 points. Illinois is rated as “leans Republican” by Charlie Cook.

Historically, poor presidential approval ratings are the single biggest indicator of midterm losses for the president’s party. And if that pattern continues and Obama’s ratings continue to flounder in the mid-40s, it’s going to be a catastrophic midterm election for Democrats in the Midwest — and in a lot of other places too.