There’s been a lot of talk about how Mitt Romney “won” last night’s presidential debate.

But in fact, Mitt Romney didn’t win the debate, Barack Obama lost it. There’s a difference. And that difference may have just handed Barack Obama the election.

As Roger Simon from Politico put it:

It’s not that Romney’s performance was perfect or polished – – it wasn’t – – it’s just that Obama’s was so mediocre.

Romney won by default.

Why? What happened?

Before we get into that, let’s define “winning.”

Unfortunately, who wins and loses a presidential debate isn’t really judged on substance. It’s judged on the look and feel of the entire thing. Who handled themselves better. And in that case, it was Mitt Romney.

As everyone’s noted, the President seemed slightly removed, while Romney was overly-engaged. Romney’s rapid-fire speaking style throughout much of the debate was risky (never, ever have anything with caffeine right before you go on TV – and I don’t buy that his diet Cokes are caffeine free; I do a good deal of TV, that man had something caffeinated right before going on).

So, Romney was less boring than the President during an incredibly dull debate, and in American terms, that means Romney “won.”

But there are a few interesting wrinkles here.

1. Romney only won because the President lost.

2. Romney lost on substance.

Let’s deal with the first. As Simon points out, Romney only won because the President’s performance was lackluster, and far below his perceived abilities.

[H]e let Romney get away with a lot. “Mr. President, you’re entitled to your own airplane and your own house, but not to your own facts,” Romney said in one of the few zingers of the debate. Couldn’t Obama have replied in kind? Obama could have said something like: “And you, Gov. Romney, think you’re entitled to car elevators and Swiss bank accounts!” Too nasty? Too unpresidential? OK, you may be right.

It’s quite a knock on Romney, in fact, but most analysts don’t think he bested the President, but rather that the he only won because the President didn’t really try. That means that whatever gains Romney gets from the debate, they don’t wipe out the underlying sense that he’s still not as presidential, as ready for the job, as Barack Obama.

Or to paraphrase: It says little about your qualifications when you win by default. And this debate was supposed to prove that Romney had presidential merit. I don’t think it did. And that takes us to our second point… Substance.

On substance, the President won. Oh, don’t get me wrong, Romney presented a boatload of facts, giving the impression that he’s well-versed in the kind of detail work necessary to be president. (Though, in fact, Romney, again, did not provide much detail at all about WHAT he plans to do in office, including on health care, where we still don’t REALLY know his plan at all.)

The only problem: His details were wrong.

The most glaring error, right off, was Romney’s claim that his health care plan won’t leave people with pre-existing conditions behind. Even Romney’s advisers had to admit after the debate that Romney was wrong. Most people with pre-existing conditions are on their own when Mitt Romney repeals their existing protections under Obamacare.

Then there was Medicare. Romney was happy to repeat the talking point, over and over again, with no challenge from the President, that Barack Obama “took” $716 billion from Medicare to pay for ObamaCare.

Actually, Barack Obama told hospitals, doctors and insurance companies that he was going to stop paying their exorbitant charges, and start paying them a more reasonable rate for the same services we’ve always been getting. That’s it. The only difference between Romney and Obama on this is that Obama wants to pay less for it, and Romney wants to pay more FOR THE EXACT SAME THING. (And don’t even get into the fact that Romney’s running mate, Paul Ryan, adopted the same “cuts” as Obama.)

The President didn’t say any of this. That’s why he “lost.” By default, not by defeat.

Igor Volsky at ThinkProgress has another 27 important facts that Mitt Romney got wrong last night.

The larger question is why President Obama let Mitt Romney win. I suspect because Obama was under orders to not sink to Romney’s level, not sully the Obama “nice guy” brand, and not elevate Romney by getting into a back and forth that would put the two on the same level, making Romney seem presidential in the public’s eye.

And in the end, perhaps Team Obama was right. It’s often been said that debates don’t have a great impact on the race. And in this race, where few people remain undecided, the impact may be even less. From Nate Silver:

There may be some mitigating factors for Mr. Obama. First, although the conventional wisdom was that Mr. Obama had a lackluster performance throughout most of the debate — he certainly had an extremely cautious and defensive strategy — there were few obvious moments in which he said things that will make for compelling YouTube clips or cable news soundbites. Second, head-to-head polls throughout the election cycle have been hard to influence for any reason. There are few undecided voters remaining — and undecided voters may be less likely than others to have actually watched the debates.

I suspect the Obama people told the President: You’re ahead, don’t screw up. And the President didn’t screw up. Mitt Romney needed a knock-out during this debate, and he didn’t get it. More Nate: