What can you say about a debate where that was the line of the night? Not much. It's difficult to believe that the debate will do much for Trump in terms of closing the gap with Biden. Probably the reverse. The instant polls for what they're worth:
A CBS News instant poll finds 48% think Joe Biden won tonight’s debate, 41% think Donald Trump won and 10% think it was a tie.
A CNN instant poll finds Biden won, 60% to 28%.
David Frum thinks Trump did have a theory of the debate but that it was all wrong:
"President Trump arrived at the first debate with a theory and a plan. The theory was that American voters crave dominance, no matter how belligerent or offensive. The plan was to hector, interrupt, and insult in hope of establishing that dominance.
His theory was wrong and his plan was counter-productive.
Trump walked onto that stage in Cleveland 7 or 8 points behind, because the traditional Republican advantage among upper-income and educated voters has dwindled, because non-college white women have turned against him, because he is losing older voters to his mishandling of COVID-19, because the groups he needs to be demobilized—African Americans, the young—are up-mobilized. On the present trajectory, nearly 150 million votes are likely to be cast in 2020. If Trump wins 43 percent of them and Biden 50 percent, not even the Electoral College can convert that negative margin into a second Trump term.
He needed to do something to change that reality.
Instead, he talked to Facebook conspiracists, to the angriest of ultra-Republican partisans, and to violent white supremacists. He urged the Proud Boys to “stand by” because “somebody’s got to do something” about “antifa and the left.” He refused to commit to a peaceful transfer of power in the (likely) event that he loses. He threatened months and months of chaos if the election does not go his way.
Trump yelled, threatened, interrupted—and changed nothing. All he did was confirm the horror and revulsion of the large American majority that has already begun to cast its ballots against him."
That seems about right to me.
Josh Marshall's take is similar:
"I worried what this momentous night would bring. In the event I think it was somewhere between bad and disastrous for President Trump.
The most important fact about this debate is that going into it President Trump was clearly behind. He needed to shift the dynamic of the race, force some major error, introduce some new factor. That didn’t happen. I saw nothing tonight that seems at all likely to improve things for President Trump. Nothing.
Biden did fine. Not great. But fine. I’d say he had a B performance with some B+ or even A- minus moments. But for him that’s fine. He’s ahead. He’s not running as best debater. He’s not running as most dynamic figure. He’s not competing for most unstable affect. He’s running as the guy who will end the nightmare. If that’s the goal he turned in just the right performance.....
There are definitely people who think Biden didn’t seem strong enough reacting to or containing Trump’s tirades. Basically I don’t think this is right. Clearly Biden isn’t really quite able to keep up with Trump’s antics. I don’t say that because of age. It’s just characterologically beyond him, for better or worse. But Biden’s not running for arguer. He held his own and simply showed himself to be a very different kind of person, a very different kind of potential President. That’s a win for him."
Again, seems about right to me. It'll be interesting to watch the polls in the next few days to see what effect, if any, the debate has on the race.