I think the South is the one region (with the exception of Florida) where Democrats win statewide or in federal races on the basis of personality and not so much party.

Party affiliation helps Dems on the coasts and in some parts of the Midwest, but in the South the Dem brand is generally regarded with mistrust on the statewide level.

Landrieu is winning because voters trust her as a tried-and-tested personality, as opposed to the party-switching Kennedy. Party-switching rarely works (e.g. Governor Connelly in Texas); in the event (e.g. Senator Shelby in Alabama) it works fine, the candidate has his (or her) ear to the winds of change and not to the plaintive ramblings of Karl Rove!