Liberals say that it has been OK to classify yourselves as a minority if you have "one-drop" of minority blood

I guess that I missed the memo that it was OK to classify oneself as a minority with "one-drop" of minority blood.  I really get the impression that this is just trying to cover liberal's tracks on Elizabeth Warren and give her cover.  It seems that if I had done that (and I am 1/32nd American Indian), there were be few claiming that was the right rule to use.  Here is a piece that refers to the "one-drop" rule.  Had I heard of the "one-drop" rule?  Sure, but I thought that this rule was surely objectionable to liberals.  Apparently, I was completely wrong.