HEMPSTEAD, N.Y. — As he prepared for the crucial first presidential debate, Donald Trump knew moderator Lester Holt would bring up the birther issue. He knew Holt would raise Trump's tax returns. And his old position on the Iraq war. None are among the voters' top concerns, but it was eminently predictable that they would be part of the debate — not least because if Holt had not brought them up, Hillary Clinton would have.

But Trump might not have predicted that Holt would leave some equally, if not more, important topics untouched. There was Obamacare, currently veering towards crisis. Immigration, including a proposed wall along the U.S.-Mexico border. The Clinton Foundation. Benghazi. Certainly a moderator can't cover everything, but those were some pretty big omissions.

Holt deserves blame for not bringing them up. But on the other hand, that is where a candidate's preparation comes in. If the moderator doesn't raise a key issue, the candidate does. And Trump didn't.

"The wall is a very important issue, and I am surprised that it wasn't brought up, frankly," one of Trump's key supporters and advisers, Sen. Jeff Sessions, said after the debate. "Also, they didn't bring up the Clinton Foundation. I mean, goodness gracious. So I thought there were a number of issues that could have been brought up that would have been troubling for Secretary Clinton that were not brought up."

Later, I pressed Sessions a bit, asking why Trump didn't raise them himself.

"Look, whenever I've done a debate, I can't sleep at night thinking of things I shoulda, coulda said," Sessions said with a laugh. "So if you think you're so good at it, you try it. I mean, it's no fun."

Trump began the debate well. He approached Clinton aggressively and made his case on the issue of lost American jobs. Clinton countered with a tired-sounding critique of what she called "Trumped-up trickle-down" economics, and an equally tired spiel on policies like heavily-subsidized clean energy as a partial fix for an ailing economy.

Things were moving in Trump's direction. "Independents are closer to Trump than to Hillary," tweeted GOP strategist Frank Luntz, who was holding a focus group watching the debate in Philadelphia. "Trump is doing better with undecideds than even with Trump-leaners. He is actually winning."

But not for long. Early on, Clinton included her first personal jab at Trump, slipped into an answer on the economy. "Donald was very fortunate in his life, and that's all to his benefit," Clinton said. "He started his business with $14 million borrowed from his father…"

Now, Trump's team knew going in that Clinton would try to get under his skin. And the easiest way to get under Trump's skin is to cast some sort of aspersion on his business, his brand, or his career. The question was whether Trump would have the discipline to ignore or brush off such attacks and stay focused on his message.

He didn't.

Trump took the bait, saying his father in fact gave him "a very small loan" in 1975. And after that Trump took virtually every other morsel of bait the Clinton, or Holt, offered him the rest of the night.

Trump went on and on about his taxes, revealing that "I'm extremely underleveraged," which surely cannot be an issue of great voter interest. Worse, Trump did not refute Clinton's charge — reminiscent of Harry Reid's no-evidence attack on Mitt Romney in 2012 — that Trump pays no federal income taxes.

"That makes me smart," Trump said, which sounded, if anything, like a confirmation of Clinton's accusation.

Then Trump took the bait on birtherism. And then Iraq. On the birther question, there wasn't a lot Trump could say, so a debater's instinct would be to cover as little as possible and move on. On Iraq, Trump actually had a case against Holt's charge, but again went on and on, adding the relatively new wrinkle that he told Sean Hannity about his opposition to invading Iraq before the fact. Trump said Hannity's name seven times.

As the debate progressed, Trump got more and more bogged down, and less and less disciplined.

"Trump could be crushing Hillary right now if he wasn't so thin-skinned," Luntz tweeted from the focus group in Pennsylvania.

Just a few hours earlier, before the debate began, Trump's team exuded confidence. Well, confidence with one caveat. Trump knew what to do to win, they said, and he was prepared to do it, and doing it was well within his capabilities. The only question was whether Trump would actually do it.

"How confident are you?" I asked a member of the Trump circle about an hour and a half before the debate.

"On a scale of 1 to 10, with 10 being he crushes it, and 1 being the campaign ends tonight — a 7.5 or 8," the person said.

Others in TrumpWorld, at least the extended circle around the Trump campaign, expressed an even higher level of confidence. Some close to the campaign suggested that Trump had pulled off a successful rope-a-dope operation, hinting to the world that he hadn't done much preparing when in fact he had prepared intensely, if unconventionally.

And besides, they said, Trump didn't have to match Clinton fact-for-fact in an old-fashioned face-off. What he really had to do was appear serious, sober, and — yes — presidential. He was ready, they said.

But he wasn't, really. Yes, Trump had some good moments. He scored on the two highest voter-interest issues, jobs and national security, and that's no small accomplishment. He also hit Clinton hard when she pulled out her talking point that she had made "a mistake" by creating a secret, unsecure email system as Secretary of State. "That was more than a mistake," Trump said. "That was done purposefully, OK? That was not a mistake…when you have your staff taking the Fifth Amendment, taking the Fifth so they're not prosecuted…"

Trump's problem was that he didn't have a lot of really good moments like that because he spent so much time talking about taxes, birtherism, and Iraq. The Clinton team wanted to distract him, to keep him on topics that hurt him — and away from topics that hurt her. They succeeded. "We were very happy with the debate," campaign manager Robby Mook said shortly afterward. "I think he was totally unprepared."

Meanwhile, those topics that could have done Trump a lot of good if handled well — Obamacare, immigration and the wall, the Clinton Foundation, Benghazi — were left untouched. Yes, blame Lester Holt for not bringing them up. But blame Donald Trump more for not taking matters into his own hands.