As I have said elsewhere, I think Clinton did great tonight. I don't see where she lost any ground.
But it is incredibly valuable for Sanders to be able to say he was on the right side of bank deregulation and on the right side for the Iraq War vote. Obama pressed the "I voted for the right war" to great advantage in 2008 (neither was necessarily right in the end). Sanders can do the same. Being able to say you actually made the right decision at the time is great. That should be taken as a signal of future good decision making.
Gun control is the only area where he has some vulnerability so it was no surprise to see Clinton go on the attack there. I am not particularly crazy about the "I represent a rural state" response, but I do not see the gun issue sticking to Bernie. He has the D- and all....
I watched the debate at the Pasadena viewing party (great Persian food restaurant!). The Sanders crowd applauded Clinton at a few points, and the messages about how better our side is than the Republicans really struck a chord with the crowd. But of course Sanders got the biggest applause of the night when he said Wall Street regulates Congress. Of the other three O'Malley probably got the most response. The spectre of Joe Biden was not as present as I thought it would be.