And that is when we'll know who actually won.
Correct. If the American people saw something in Trump's performance which had them say "I was undecided but now I think that this guy should be President" then Hillary Clinton is
fucked. There was apparently a huge audience for this debate and if the result of it is that Trump's poll numbers go up then there's really nothing that Clinton can do to win the election. It would mean that there is such an appetite for change -
any type of change - that they are voting for the guy who is promising to break the system and they have absolutely no concern who it is that's doing that or how it's being done, so Trump's lies and missteps aren't a relevant factor in their decisions.
If Trump's poll numbers start to go down, I also don't think that there's much he can do to even them out again. It will mean that when they stood together side by side, he was found wanting. Further debates and campaign events aren't going to have the same impact as the first time that most people really started paying attention and judging them as the two potential options.
One way or another, this debate decided the election.