Okay, I'm going to preface this by saying that I think this scenario is unlikely, and that it is pure speculation on my part. But while unlikely it is nonetheless a possible scenario so I thought I'd throw it out there for you to chew on.
Consider...Joe Lieberman beats Ned Lamont and wins the Senate seat in Connecticut.
Early in 2007, Don Rumsfeld quits as Secretary of Defense.
George W. Bush offers the job to Lieberman, who accepts.
Connecticut's Gov. Jodi Rell (R) appoints a Republican to fill Joe's vacated Senate seat until 2008.
Result: George W. Bush gets a "bipartisan" Secretary of Defense, and the Republican party gets a free Senate seat in Connecticut - a seat which they didn't even contest in the 2006 elections.
Just a thought. Should I go get my tinfoil hat now?

(On edit: I was just informed that pabsungenis already beat me to this theory with his post
yesterday.)
(On edit again: Now it appears that KnaveRupe beat us by
almost a week. Nice going

)