Warren is a really polarizing political figure, but so is Don. I imagine a race between the two would be quite the barn-burner, and I would look forward to it. I don't think Warren would turn off too many people who voted for Clinton, and may also bring in a few millennials who were disillusioned with the previous nominee. She isn't the strongest candidate by any stretch, but I wouldn't count her out. The left just might need a bit of a street-fighter to take on the current brawler of a president.
I could see her losing some ground off Clinton's numbers in the suburbs.
