I read somewhere that this seat has been in GOP hands since the Civil War...anyone know if that's true?
Since the current occupant is not a Republican, I guess not.
That is true. In fact, Leahy is the only Democrat Senator in Vermont history.
There have been a series of RINOs in that seat going back to at least the 1950s -- George Aiken, Bob Stafford, and Jumping Jim. Vermont was one of only two states to vote against FDR in 1936, and was of course home to Calvin Coolidge, so it does have some glory in its distant past. But not much lately.