Does Massachusetts Senator Elizabeth Warren really have Native American blood running through her veins? It's scientifically impossible to know for sure, according to a collection of leading geneticists, industry experts, research scientists with expertise in indigenous genetics and Native American leaders who spoke with ABC News. The process of tracing one's ancestry is still evolving, geneticists told ABC News, and efforts to establish genetic affiliation with an indigenous group like Native Americans are at best thorny and uncertain, and, in the extreme, offensive. Some experts were critical of Warren's press conference this week and her latest declarations. Numerous experts also...