For some people, the struggle for Black Lives and Rights (or those of women) trumps the policies of the individuals involved. Maybe Barbara Lee is so sensitive to racism that any threat to Obama (and his policies) comes back to that core value? It's easy for white people to dismiss how important racial solidarity may be to those who finally have some power and influence in a nation that treated them as objects for decades.
I listen to "Feminists" who back Mrs. Clinton and it's that same thing. For them, it's more important to just HAVE a woman in the White House. They don't look honestly at her policies or the degree to which Hillary has gone along with the worst of corporatism and militarism in order to get this close to the acme of power (in its apparent state... since after all it's really the Deep State that's running the agenda).
I am not apologizing for or excusing these behaviors. But I think before blame is cast (and so often it comes from Caucasians, particularly white males who have never had to wrestle with these constant insults to their person and life prospects), it's important to really take in WHY some people show the loyalties that they do.
In case it's not clear, I fully support Mr. Sanders.
But it's wise to try to understand people on their own terms. Casting blame just shuts up discussion and does nothing to educate.