So, thoughts about the debate:
First, nobody watched it. I think the candidates knew this, because they got a little goofy.
Yang was very likeable and entertaining. He also spoke for an entire nation when he gaped speechlessly at one of the worst questions ever asked in a presidential debate, about who they would ask for forgiveness and/or who they would give gifts to.
Warren did well, and also got some good laugh lines in. She didn't own the debate like she did some of the earlier ones, but she seemed more confident in her positions than she has more recently. I can easily imagine her recovering in the polls some.
Buttigieg seemed like he was part of the top four candidates. He had a real spring in his step. I would also expect him to increase in the polls some, were it not for the fact that he was competing for a lot of the same voters as Warren.
Sanders had a pretty bad debate early one ("I AM WHITE!!!!!"), but he got into a good boxing match with Biden on healthcare.
Biden had a good night. He never actually fell asleep, he didn't spout nonsense at any point, and he gave some cogent, forceful answers.
Klobuchar did... okay. It was a very good debate for her, but it was also a good night for almost everyone else. I'm not sure who she would be taking votes away from.
Steyer needs to go to Bed Bath and Beyond, buy everyone a damn Christmas present, and then drop out. I generally like him, but he doesn't belong on that stage.