After the first debate between Obama and Romney in 2012, it was amusing to watch Democrats, pathologically afraid of their own shadows, cower in their blankies because Obama seemed off his game. Scratch that. Was off his game. And therein lies the difference between the first 2012 debate and the first 2016 debate. When Obama first debated Romney, Obama had a bad night, Romney had a good night, the latter got some great press as a result, but in the next debates, the narrative, such as it was, returned to normal. But, since narratives are basically a minor part of presidential elections, which turn mostly on factors such as the economy in normal years (i.e., years without people like Trump on the ballot), that stuff basically didn't matter in the end. The economy was growing, and the incumbent won reelection. So, the first Obama/Romney debate was an anomalous debate that didn't really do much in the end.
The first Clinton/Trump debate? This one may really seem to matter for two reasons. First, Trump had made a lot of progress in the polls. A month or so ago, Trump looked like he was losing in a blowout election. Then, the race tightened. A lot. Then, Trump had a debate performance that made Obama's first debate against Romney look like a virtuoso performance. But why could this be so different? Because while Obama's soporific performance in the first 2012 debate was a deviation from his norm, Trump was reverting to form on Monday, as was his post-debate series of attacks on Alicia Machado. He gained in the polls by not acting like the bullying blowhard he had been for most of the campaign. Oops.
Obama walked into that first debate in 2012 as the clear leader in the race. He walked out weakened because something went wrong in an unexpected way. Trump walked into the debate having made progress, and undercut it by behaving in an expected way.
And yet, the fact that Trump had made that progress means we cannot call this the end of the line. There is a month left, and this is the most batshit crazy election we have ever seen. Aside from my usual "terrorist attack or economic downturn" possibilities for a Trump victory, we must add changes in Trump's behavior. Trump's reversion to form on Monday and since makes that less likely going forward. The guy just has a hard time controlling himself, particularly when baited, and that is sort of central to Clinton's point. But at this point, anyone who claims to have seen the twists and turns this campaign has taken is bullshitting you. The odds favor Clinton pretty heavily at this point, and the post-debate polls are showing the effects of Trump reverting to form, as I started to say yesterday. This ain't the end of the line, though. If you don't know what Trump will do tomorrow, you don't know what the effects will be. That's kind of the point of erratic behavior.