Minor correction. The VT hasn't gone 'Rat since 1958. It's been a Socialist seat since 1990.
"A socialist seat since 1990."
As I said -- Rat.
While I can imagine a "socialist" member of Congress with integrity who at times broke with the Rats, Mr. Sanders is simply a left-wing (i.e., typical) Rat. He has the full support of the Rat party, and will continue to be with the Rats when he goes to the Senate. Just because he (accurately) uses a more colorful term for himself than the typical "liberal" or "moderate" is no reason to pretend he isn't a Rat.
Obviously if a state continually elects an openly professed socialist to Congress, it is a Rat state and will elect a Rat when he leaves.