(CNN) The best way to understand Donald Trump's approach to the presidency is to think of him as what he was before politics: The star and producer of a reality TV show. Trump is forever programming the show -- aka his White House and the country -- in ways he thinks will entertain, provoke and amaze the audience.

And man, did he ever dial up a classic episode on Tuesday -- conducting an often-contentious public debate with Senate Minority Leader Chuck Schumer, D-New York, and likely House Speaker-in-waiting Nancy Pelosi over border funding, the wall and who would be to blame for a government shutdown.

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It was, without question, good TV. It was the sort of sausage-getting-made (or, perhaps more appropriately given how things transpired, not getting made) moment that the public rarely gets to see.

"We're here to have a conversation," said Pelosi at one point. "I don't think we should have a debate in front of the press."

And yet, have the debate they did! But as the three politicians were fighting -- and the fourth man in the room, Vice President Mike Pence, seemed very focused on trying to blend into the wallpaper -- something interesting happened: Donald Trump lost.

Here's how it happened (bolding mine).

Pelosi said she wanted to avoid a "Trump shutdown." Trump interrupted to note that the possibility of a government shutdown -- the federal government is set to run out of money on December 21 -- was entirely on Senate Democrats, who wouldn't support a bill to fund his border wall that he felt confident could pass the House whenever he wanted it to.

That led to this exchange between Trump and Schumer:

SCHUMER: "One thing that I think we can agree on is we shouldn't shut down the government over a dispute, and you want to shut it down."

TRUMP: "The last time, Chuck, you shut it down, and then you opened it up very quickly. I don't want to do what you did."

SCHUMER: "Twenty times you have called for, 'I will shut down the government if I don't get my wall.' None of us have said it."

TRUMP: "You want to know something? ... I'll take it. You know what I'll say? Yes, if we don't get what we want one way or the other, whether it's through you, through military, through anything you want to call, I will shut down the government."

SCHUMER: "We disagree."

TRUMP: "And I am proud ... I tell you what, I am proud to shut down the government for border security, Chuck, because the people of this country don't want criminals and people that have lots of problems and drugs pouring into our country. So, I will take the mantle. I will be the one to shut it down. I'm not going to blame you for it. The last time you shut it down it didn't work. I will take the mantle of shutting down and I'm going to shut it down for border security."

That last line from Trump is an absolute dagger politically.

In both the run-up to and the aftermath of government shutdowns, both parties work very, very hard to blame the other side. The reason is simple: People hate Washington and think it doesn't work for them. When a shutdown happens, all their worst fears are realized. They get angry. The look for someone to blame. And that someone is always one of the two political parties.

Given that reality, why say -- and I am paraphrasing -- if I don't get what I want, I am going to shut down the government? The answer is that you wouldn't. Or at least no normal politician would.

Trump is, as we know, not a normal politician. So why did he give Democrats such a gift in advance of the looming shutdown? Two reasons, I think.

1. Schumer and Pelosi got under his skin

Remember that Trump -- in his past life and in his presidency -- is used to telling people what to do and having them do it. He's set his White House up that way; he's surrounded primarily by family members and staffers who, generally speaking, tell him what he wants to hear.

From the start of the public side of this meeting with Pelosi and Schumer, it was clear that wasn't the way this one was going to go. Schumer mocked Trump for touting Republicans' two-seat Senate gain in 2018 ("When the President brags he won North Dakota and Indiana, he's in real trouble") and Pelosi scolded him for characterizing her relative strength within the House Democratic Caucus.

Trump doesn't like that and isn't used to it. And he reacted poorly. He lost his temper a bit. He let Schumer goad him into owning a possible government shutdown.

2. Trump believes his base wants the wall more than anything

While I do think Trump let his ego and his temper get the better of him, I also think he has a deep belief that building the wall is keeping a promise of deep import to his base. Remember that his promise of a wall -- and his oath to get Mexico to pay for it -- was what sparked his longshot presidential campaign way back in the summer of 2015.

Without the wall, it's uniquely possible that Trump never moves from the less-than-zero spot he began at in early 2016 polling. Trump knows that the GOP base is deeply invested in the construction of a full southern wall and feels it is his duty to at least make good on that one campaign promise.

And there is, without question, a bloc of Republicans (elected officials and base voters) who cheered Trump's performance with Schumer and Pelosi and who believe that a government shutdown might be a necessary evil to get what they want out of Congress.

The problem for Trump is that his loyal base isn't enough to get him re-elected. Or, as the 2018 midterms showed, to hold onto the House or a slew of other down-ballot races that went against Trump last month.

Now anyone who watches TV in the next 24 hours -- so, most of us -- will see that clip of Trump promising to own the shutdown. Trump loves showing how politics really works. But this episode of his ongoing reality show made him look bad. And he hates that.