All I'm saying is that throwing everything they had on Obama at the wall and not caring what sticks didn't pay off for them.
That's because for a criticism to stick it has to be at least somewhat connected to reality. The idea of Obama being a socialist Kenyan muslim is just flat out demonstrably wrong. Still, it worked well enough that a sizable portion of the GOP electorate believes it, but not enough to persuade any sensible people.
The problem for Sanders is that he really does hold beliefs that scares the beejeezus out of a lot of swing voters - large tax increases being just one such issue. Now personally, I support larger taxes, universal health care, free universities, a radical new approach to global warming etc., but I'm realist enough to know that you cannot yet win a presidential election on that platform - unless your opponent is a radical, which will likely be the case in this very election. Against a generic republican Sanders would get trounced.
BTW, this is what Trump has been so good at this cycle: to narrow in on a candidates perceived weakness and just hammer it endlessly ("Low Energy Jeb", "Lyin' Ted", "Little Marco"). It has worked because it reinforces a belief about these candidates that already exists (that Jeb is boring, that Cruz is a slezeball, that Rubio is a big gullible kid, etc).
