I have no reason to doubt Elizabeth Warren's assertion that she grew up thinking that she had Native American ancestry. What probably happened is that a story got repeated wrong. One of her ancestors was part of the Trail of Tears - as a guard instead of a participant. After a hundred years or so he was probably turned into an Indian himself. This happens in a lot of families.
The real question is what Warren did with this. Did she use this supposed ancestry to advance her career? Did someone once say to her, "We'd love to hire you but your degree is from a middle-of-the-pack law school. Can you qualify as a minority?"
Affirmative Action programs were meant to help people who had been held back by overt discrimination. The blond, blue-eyed Warren obviously never suffered any discrimination because of her untraceable Indian ancestry. Even if she does have a drop of Indian blood, it would not have made the slightest difference in her upbringing or opportunities. So, if she listed herself as a minority to advance her career she was deceiving people and possibly taking a stop that could have been filled by a real minority.
We don't know if she did because the records are sealed.
This has little real significance to her Senate qualifications but, in an age where Romney's treatment of his dog in the 1980s is considered relevant, nothing seems to be off-limits. It does reflect Warren's values more than Romney's dog does.
Like many conservatives, I am overjoyed to see Warren fall. Her pitch for higher taxes last Winter was misleading and potentially harmful so anything that takes her down is welcome, especially if it is self-inflicted.