I think Sanders used it in the Northern European sense, and, really, we are all Social Democrats in that sense. But you are right that that is the self-imposed label that dooms him. He is trying, however, to get that meaning adopted by the mainstream to take away its sting. Ours is a Social Democratic Republic (and Representative Democracy), but most people don't recognize it for what it is.

A well reasoned argument is like a diamond: impervious to corruption and crystal clear - and infinitely rarer.

Here, as elsewhere, people are outraged at what feels like a rigged game -- an economy that won't respond, a democracy that won't listen, and a financial sector that holds all the cards. - Robert Reich