He's a three term Senator elected to that body as an Independent that has always caucused with the Democrats (as he did in the House befor that), is currently given by the Senate Democrats the position of Chair of the Health, Education, Labor, and Pensions Committee, and was the #2 Democrat in the last two Presidential nominating contests.
Anyone can try and get the Democrat nomination for president, they don't limit it to card carrying Democrats.
Bernie Sanders identifies as a Democratic Socialist. You can, of course, call him whatever you want, but it won't make him identify himself differently.
> Anyone can try and get the Democrat nomination for president,
Yes, and lots of people do.
People who aren’t accepted by other Democrats as part of the team don’t end up with large blocks of convention delegates and a major role in shaping the rules going forward due to that.
> they don't limit it to card carrying Democrats
No such thing exists, unless you are talking about people who pay membership fees to the DNC, but that's a pretty narrow definition.
