Biden may have helped himself last night with his sheer adamance that he’s not getting out since he’s basically in a game of chicken with his own party — the less likely it seems that he’s going to go, the harder it makes it on everyone to publicly call on him to go. But it wasn’t, as Phil and Mark note below, a reassuring performance.

If we just take his debate explanations alone, these are things we never hear from a sitting president. The idea that he was too tired and too rattled to turn in a coherent performance is, in itself, a damning concession. The word “exhausted” came up several times. It was easier to miss this in response to Stephanopoulos asking when he realized he was having a bad night:

Well, it came to me I was havin’ a bad night when I realized that even when I was answering a question, even though they turned his mic off, he was still shouting. And I — I let it distract me. I — I’m not blaming it on that, but I realized that I just wasn’t in control.

A president of the United States should be able to handle someone yapping at him off mic. Regardless, Biden’s most notorious line of the night, the “beat Medicare” riff, came early on before the attempted cross-talk got heavier in the middle of the debate.

At the end of the day, there’s no benign explanation for Biden’s performance. Either he’s too fragile (too tired, too easily distracted) to perform at a high level, or too addled. The latter is worse, but neither is good.