A Democrat in name only that voted for the democratic party line more than any other democratic senator except one. I would say Sanders is an independent in name only, he even caucuses with the democrats. Caucusing with one or the other party eliminates the independent status. Sanders has chosen a side as has King.
Both Sanders and King are counted as democrats in most reports, which is why it is reported you have a 50-50 senate, 50 republicans, 50 democrats. Not 50-48-2.
Of course it's all semantics anyway.