CNBC's BRIAN SULLIVAN: Is there anyone else in the Senate that is a professor? ELIZABETH WARREN: I don't think so. ... We had the big crash in 2008. What does everyone say about it? They say too much concentration in financial services creates too big to fail. It puts us at bigger risk. And what's happened since 2008? The four biggest financial institutions are now 30% bigger than they were in 2008. The central premise behind a 21st century Glass-Steagall is to say if you want to get out there and take risks, go ahead and do it. But ... you can't get access to FDIC insured deposits when you do. That way ... at least one portion of our banking sector stays safe. From 1797 to 1933, the American banking system crashed about every 15 years. In 1933, we put good reforms in place, for which Glass-Steagall was the centerpiece, and from 1933 to the early 1980s, that's a 50 year period, we didn't have any of that - none. We kept the system steady and secure. And it was only as we started deregulating, [you hit] the S&L crisis, and what did we do? We deregulated some more. And then you hit long-term capital management at the end of the 90s, and what did we do as a country? This country continued to deregulate more. And then we hit the big crash in 2008. You are not going to defend the proposition that regulation can never work, it did work. SULLIVAN: I didn't say regulation never worked, Senator. By far and away, and I agree, there were fewer bank failures in that time after Glass-Steagall. ELIZABETH WARREN: Fewer," as in, of the big ones, zero.