With today's Quinnipiac poll showing Rob Simmons leading Chris Dodd 43-42 in Connecticut, I believe that makes Dodd the fifth incumbent Senator up for reelection next year who has not announced his retirement to trail in a head to head poll.
Two of the others were ours:
-We showed Roy Cooper leading Richard Burr 39-34 in North Carolina.
-We had Bill Owens leading Michael Bennet 44-41 in Colorado. An Owens campaign seems very unlikely.
And the other two were Kos'
-Janet Napolitano led John McCain 53-45 in an October poll, although it seems pretty clear now this contest won't happen.
-Sarah Palin led Lisa Murkowski 55-31 in an Alaska primary match.
Am I forgetting another poll that showed an incumbent losing? I know there's been some less than encouraging ones for Arlen Specter but don't remember one where he was actually down in a head to head contest, although I'm sure if you polled it today he'd trail Pat Toomey in the GOP primary.