Democratic U.S. Senate candidate Elizabeth Warren arrives in Springfield today, along with 5,000 delegates to the state's Democratic party convention.  Ahead of the convention, Warren has written a letter to her supporters, addressing the controversy over her claimed status as a Native American.  Warren says a child never asks their grandparents for legal documentation of their stories.  Warren blames Senator Scott Brown and Republicans for orchestrating an attack on her family.   Meanwhile, Native Americans are planning to protest against Warren at tomorrow's convention.  THey say they're angry over the way she has handled talk about being part Cherokee.