There was the guy in Kentucky or Tennessee early this century. I'm sure RL remembers who it was. He was elected as a Republican but a while in switched to Democrat [or was it an Independent who caucused/voted with Dems? Doesn't really matter which as long as he goes with them].
Leiberman is kind of the same thing. He lost the Dem primary in his state because the Dems didn't like him anymore for being too centrist basically. He ran as an Independent and won. He still mostly votes Democratic but not always.
