I think we all agree that victory exists in opposition to failure. I'm going to argue that both Sanders and Clinton had victories. I think however that Sanders won the most meaningful one.
Secretary Clinton was victorious in looking poised, prepared, and professional. She showed that all the negative attention she's been getting hasn't diminished her likability among Democrats.
Senator Sanders for the first time was in a national debate running as a Democrat. He had to answer question going to his origins and he dealt with them admirably. He finished the debate by being viewed warmly by our party as a whole as a great spokesperson for us. He reached many Democrats who had little idea as to who he was and he's now on their radar after having made a favorable impression.
Young voters, and Independents, got to learn more about the candidate who's been doing extremely well with their demographic. They now have had confirmed his authenticity as the kind of candidate they want to see on the ballot. They represent important "stealth" votes, in key states, that normally can't be counted on for much turnout. Sanders can get these voters to show up while other candidates just don't appeal to them.
We're going to be hearing lots more about issues important to these voters, and Sanders has wisely played the long game by laying out in a deliberate fashion the parts of his platform that win them over to our side. It's also going to become more clear as to why we need the unique appeal of Senator Sanders to voters we've let slip through our fingers.