Biden's problem isn't just that he had a terrible debate.

It's also that he probably did about as well as he can.

So far, there haven’t been many apologists for Joe Biden’s wretched debate performance. However, more will emerge if (as I think likely) hope of replacing him on the ticket fades.

It’s one thing to criticize the performance of a candidate you hope you can push out the door. It’s another to criticize the performance of a candidate you’re stuck with.

So far, two lines of apology have emerged. The first is that Biden had a bad cold. But all voters (and non-voters) have had bad colds. They aren’t fun, but they don’t interfere with one’s ability to state a coherent thought or finish a sentence.

The other line is that incumbents typically struggle in their first debate. That’s true. With the exception of Bill Clinton, I think all of them have.

But there’s struggling and there’s imploding. The likes of Gerald Ford, Ronald Reagan, the two Bushes, Barack Obama, and Donald Trump struggled. Biden imploded.

Furthermore, the reason for Biden’s woes are entirely different, and far more damning, than the reason for past incumbents’ struggles. I believe the problem for other incumbents was that, having served as president, they figured they knew what to say without doing much preparing. And due to their status, they weren’t prone to being coached and contradicted. Thus, they weren’t well prepared to deal with the blows their opponents landed.

In Biden’s case, the problem was the opposite. Fearful of confirming the widespread suspicion that he couldn’t get through a debate without embarrassing himself, Biden reportedly prepared intensively for a week. During that time, I assume he was fed talking points on every issue likely to come up. And it was clear from the debate that some of his planned responses contained multiple parts.

Biden was at his worst when, in answering questions from the hosts, he tried to serve up multiple-part answers. He had trouble remembering his lines.

Biden was best when he was firing back at Trump. I noted this disparity here, attributing it to Biden’s anger at Trump which, I speculated, enabled him to roll back the years.

I still think that’s part of the explanation. However, a friend came up with a better one. When Biden was responding to the hosts, he was trying to remember lines. When he was firing back at Trump, he was answering more spontaneously.

The difference between Biden’s debate woes and those of incumbents past has two important implications. First, voters can forgive a bad debate performance if they believe it was the result of over-confidence and under-preparation. It’s hard to forgive a bad performance if it’s seen as due to a lack of the mental capacity to do much better.

Second, most of the previous incumbents were able to bounce back to one degree or another in subsequent debates. Reagan certainly did. So did Obama, with a big assist from Candy Crowley.

But if Biden’s woes were due to inability to remember lines and deliver them coherently, a bounce back will be difficult. My advice would be to prepare less.

But Biden over-prepared for a reason. It’s doubtful he could coherently answer policy-based questions without a considerable amount of preparation.

I’ll conclude with a few words about Trump’s performance. In my view, it was good only in comparison to Biden’s.

What helped Trump was the simplicity of his talking points. On most topics, there were just two of them.

First: We had the greatest [fill in the blank] ever during my administration. No one could believe how successful I was.

Second: We have the worst [fill in the blank] ever under Joe Biden. It’s terrible how bad the [fill in the blank] is. The rest of the world is laughing at us.

I’m not saying Trump couldn’t learn and deliver more substantive and complex lines. I assume he could, if he really wanted to. And he certainly could do it better than Biden.

But against an opponent capable of delivering even an average performance, Trump would have to raise his game. Otherwise, his answers would be ridiculed as braggadocio, devoid of fact and evidence (if not flatly false).

Fortunately for Trump, he’s unlikely to face such an opponent.