Debates are performances.
Biden gave the worst performance in the history of debates, and he had to drop out of the election as a result.
The first time round Trump rode to the presidency on the back of his debate performances. His greatest skill was to put everyone around him on tilt by becoming the personification and embodiment of an internet troll. It proved a highly effective strategy. And it was all performance.
This time the expectation of many was that Harris was not up to the task and her performance would prove it ("Why is Harris afraid to debate?" "Isn't her nervous laugh weird" "Why does she need to prepare so much? It will hurt her.") But the reality is that she significantly outperformed Trump last night. As the old saw goes, Trump's failure to prepare was preparing to fail. His over confidence combined with his inability to avoid every trap set for him (all of which were predictable - let's talk about crowd size) led to a pretty unhinged performance last night (I heard it on TV). Harris was very successful putting Trump on tilt and appearing to be the only adult on stage. Even her "isn't he cute" condescending smirk pose was effective.
Trump was so on tilt that he failed to put Harris on the spot for not answering any difficult questions. Never mind that never in the history of debates has any candidate, ever answered a difficult question, Trump's one job was to press her on Biden's policies and he failed miserably to do so. At the very end he made a weak attempt to bring it back to that, but by then the damage was done.
Now, what does it mean? It is hard for me, or anyone that posts on this forum, to say because we are so entrenched in our positions. I cannot project to the mind of the undecided voter, who is almost certain to decide this election. But if I am a Trump advisor this morning all I am thinking about is damage control. Nowhere near as bad, but kind of like Biden advisors were after the last debate.