An Open Seat in Vermont... Could be a tough race.

[zorkpolitics]

At least one Democrat, former St. Sen. Peter Shumlin Speaker Pro Temp, has announced he is seriously consdiering running. 
Assuming he syphons some support from Sanders, it  might be come competitive, still Sanders has the edge at this point.

[○∙◄☻¥tπ[╪AV┼cVê└]

If it looks like some Democrat is trying to play spoiler, Bernie could just run for the Democratic nomination to knock that Democrat out.

[Fmr. Gov. NickG]

I can't imagine why any serious Democrat would run in this race.   They would be a national embarrasment...when was the last time a major party nominee got single digit support in  a Senate race?....at least Jack E. Robinson got 13%.

That said, I'm almost certain Sanders would never run as a Democrat.