The fundamental confusion that caused much of the media to botch their debate coverage is that they thought the story of the last few months was Hillary collapsing, rather than Bernie rising. All the media has been covering are her problems and scandals, so when they saw her poll numbers declining they thought their coverage was the explanation. Stories talk about the potential for a Hillary ‘implosion’, whatever that means, and speculate about Biden joining the race if she screws up, since of course they can’t imagine Sanders as an alternative. So when Hillary got up and showed herself to be competent and well-spoken and not much weighed down by their bogus scandals, they said “Wow, she is so great, defying expectations! What a win for Hillary!” In reality, as poll after poll shows, this race has never been about Democrats souring on Hillary, it’s that they really like Bernie. Everyone outside of the pundit bubble already knew that Hillary was competent and well-spoken, and few Democratic primary voters bought into the silly email and Benghazi ‘scandals’ in the first place. For most people, who have not been following the race very closely up until now, the big story was “Hey, look at this Bernie Sanders guy!” After months of little coverage, and with most of the coverage there was constantly emphasizing his ‘fringe’ status and downplaying his chances, people got a chance to listen to his message for themselves, and unsurprisingly, it hit home with a lot of them.
I’m not exactly sure what it means to have ‘won’ a debate. There’s no objective criteria to talk about. What matters is what effect the debate has on the people watching. I can’t imagine anyone whose mind would have been changed by Hillary’s performance. People know her and have opinions about her, and nothing she said on stage shifted those opinions much. On the other hand, there were a lot of people turned on to Bernie by the debate, simply because they got to hear him speak for once.