I might as well confess my biases here. I tend to favor debaters who appear to know what they are talking about, have a good command of facts and serious understanding of policy. Even if I don't agree with candidates, I am inclined to cut them some slack if they make a good, evidence-based case for what they want to do.
Thus to me Ronald Reagan's performance against Carter is sort of the gold standard of debate. A number of people have commented that, although there was pervasive discontent with how the country was doing, many people were afraid Reagan was a crazy fanatic. The debate convinced them otherwise. Speaking for me, I was quite impressed when he regularly countered Carter's accusations and attempts to paint him as extremist with calm facts, even to the point of chuckling and says "There you go again," after several such accusations. Not everyone agreed with me. My civics teacher at the time said he would never trust anyone who chuckles while talking about nuclear war. But there you have it.
On the other hand, Sarah Palin is a sort of anti-gold standard. Hers was the most painful debate performance I have ever seen. My impression watching the Biden-Palin debate was that it was between two candidates, one of whom had a serious, in-depth understanding of policy, and the other one of whom was reciting canned talking points. And, in fact, some accounts afterward say that that was exactly what she was doing. Not everyone agreed with me. Palin supporters thought she did great. But a majority clearly saw Biden as the winner. To me, it looked like a high school athlete trying to compete against pros.
Well, Trump wasn't Ronald Reagan. But he wasn't Sarah Palin, either. Hillary started with what sounded to me like a lot of glittering generalities without much substance behind them, while Trump came out with what sounded like facts, even if some of them actually were not true. On the other hand, if you had turned the sound off, Hillary would look like a normal person, while Trump's facial expressions and body language were exaggerated and clownish and did not look worthy of a leader of the free world. And as the evening wore on, Trump started shouting and showed that he could be provoked. Clinton stayed calm. And while the audience was told to be quiet there were some lines that got laughter and some that got applause. Trump drew first blood on applause, saying he would release his tax returns when Hillary released her e-mails. But I would call the most noteworthy event of the night Trump saying he had the better temperament after a rant that rather strongly proved the contrary. That got a good laugh too, but not an intended one.
So I would say advantage Trump earlier on and advantage Clinton later. But never a real blowout. My side, obviously, exaggerated every one of Trump's errors and failing. But even Trump's side seems to think he should have prepared better.
The big question, of course, is now what. There are two more debates to go. What will happen?
The cynical take is that whoever lost the first debate will necessarily have to be declared the winner of the second, with the original winner making a comeback in the third. That is how the media always spin debates in order to maintain drama and suspense.
My prediction for the narrative, based on every election since 2000, is that Trump will be deemed to have improved substantially in the second debate, and then Clinton will be seen as pulling off a needed comeback in the third. Note that this is my prediction for the narrative. It doesn’t matter if Trump spends the second debate yelling into his cell phone about how he won’t pay construction workers, or if Clinton suffers a stroke in the third debate. In the second debate it is necessary that Trump be seen as redeemed, so if he spends the entire debate ignoring the moderator and yelling about his refusal to pay a bill he’ll be called “bold and unconventional” for doing so. In the third debate, if doesn’t matter if Clinton goes into a coma, the narrative demands a comeback, so she’ll be seen as “incredibly graceful as she soldiered on until medical personnel intervened.”On the other hand -- well, Trump's supporters say that he has to prepare better, but it is not clear whether he is even capable of preparing. Remember all those comments how he has an incredibly short attention span and is incapable of focusing for more than a few minutes on subject other than his own self-aggrandizement. That makes debate prep really hard. And the next debate will consist of ordinary citizens asking questions. I have seen debates of that type and don't like the format much. Ordinary citizens' questions tend to be quite narrowly focused on issues that affect them personally rather than ones of national importance. But the result is to give a clear advantage to the wonk who had an incredibly fine-tuned knowledge of policy.* Others (cannot find link) have suggested that the town hall format plays especially poorly for the sort of temper and dominance displays that are Trump's stock-in-trade.
And finally, there is the question of how much it matters at all. After all, the general consensus is that debate rarely do more than briefly move the needle. Hillary's debate bump is already looking to be smaller and shorter-lived than her convention bump. On the other hand, we are now in the home stretch, with just over a month to go, at a time when every little flicker in opinion polls really does matter. Complacency (or despair) is still premature. But it is nowhere near as premature as it was a few months ago.
General forecast: A very stressful month ahead.
*This approach also may have an inherent bias toward Democrats. Can't find the link, but when reporters switched which side they covered, they were particularly impressed by that. Democratic voters have specific concerns that they want the candidates to address, while Republican find the whole idea of government addressing people's problems repugnant and address ideological generalities instead. The town hall format focuses on people with specific concerns they want the candidates to address.