Last night, Donald Trump and Hillary Clinton did back-to-back appearances at a town-hall-style event on national security, and while there has been a lot of deserved criticism of the job Matt Lauer did moderating, what’s more important is what Trump said and did, and what the implications are for the upcoming debates and the presidential election more broadly. Even though the discussion was focused on a narrow range of topics, this one-hour event showed us the entire election in microcosm, in ways that are both maddening and terrifying.

Fifteen months after he announced his candidacy for the presidency, we’ve almost run out of ways to describe what Trump represents. He is, without a doubt, the most dishonest candidate to run for the presidency in modern history, and perhaps in all of American history. It isn’t even close, and that should be beyond dispute by now. It isn’t just about his habit of stating alleged facts that are demonstrably untrue, and continuing to repeat them even after it’s been pointed out that they’re false, though that’s part of it. It’s also about the sheer volume of unreality he delivers, as though he’s trying to drown us all in a river of bull that moves so fast that truth itself begins to seem almost irrelevant.

I’m going to take two exchanges from last night’s forum to show you what I mean, the first of which concerns Trump’s “plan” to defeat the Islamic State. For some time now, Trump has been saying that he has such a plan, but he doesn’t want to reveal it because then the terrorists would know what’s coming. “All I can tell you it is a foolproof way of winning,” he has said. Then, yesterday, he announced in a speech that when he’s inaugurated, he’ll order the Pentagon to come up with a plan to defeat the Islamic State in 30 days, which would seem unnecessary if he already has a “foolproof” plan. Here’s what happened at the forum:

LAUER: You said this. Quote, “We’re going to convene my top generals and they will have 30 days to submit a plan for soundly and quickly defeating ISIS.” So is the plan you’ve been hiding this whole time asking someone else for their plan?
TRUMP: No. But when I do come up with a plan that I like and that perhaps agrees with mine, or maybe doesn’t — I may love what the generals come back with. I will convene …
LAUER: But you have your own plan?
TRUMP: I have a plan. But I want to be — I don’t want to — look. I have a very substantial chance of winning. Make America great again. We’re going to make America great again. I have a substantial chance of winning. If I win, I don’t want to broadcast to the enemy exactly what my plan is.
LAUER: But you’re going to …
TRUMP: And let me tell you, if I like maybe a combination of my plan and the generals’ plan, or the generals’ plan, if I like their plan, Matt, I’m not going to call you up and say, “Matt, we have a great plan.” This is what Obama does. “We’re going to leave Iraq on a certain day.”
LAUER: But you’re going to convene a panel of generals, and you’ve already said you know more about ISIS than those generals do.
TRUMP: Well, they’ll probably be different generals, to be honest with you. I mean, I’m looking at the generals, today, you probably saw, I have a piece of paper here, I could show it, 88 generals and admirals endorsed me today.

Here’s the problem this presents. What he’s saying is so transparently phony that it just boggles the mind, yet you can’t do an “objective” fact-check on whether Trump has a secret plan to defeat the Islamic State, because you can’t prove that he doesn’t. But he doesn’t. I also can’t prove that every night while I sleep my dogs haven’t been painstakingly constructing a teleportation machine, then burying it in the back yard before sunrise, only to dig it up again the next night to continue their work. But it would be lunacy to assume that that’s what’s happening. Among those inclined to defend the Republican nominee, is there a single person who could say with a straight face, “Yes, I’m sure that Donald Trump is telling the truth when he says he has formulated a secret plan to defeat ISIS”?

So how should journalists deal with this? The closest thing to a solution is to ask Trump as many specific follow-up questions about it as they can. Even if he won’t tell us what’s in his plan, we could come close to exposing him as a charlatan by forcing him to add more layers of baloney to the edifice he has already constructed. We could ask things like, Is the plan written down, or is it just in your head? How many pages does it cover? Did you formulate it yourself, or did you work on it with other people? Who are those people, and can they confirm that they worked with you on it? How many hours would you say you devoted to the task?

There’s a good chance that if he were forced to answer those questions, he’d end up looking like even more of a fool as he spun out the fantasy even further. The problem, though, is that “exposing” him in this way probably wouldn’t make much of a difference, either in changing his behavior or in changing the minds of those who’ve decided they want him to be president.

Now let me point to a second exchange in the forum, when Lauer asked about the intelligence briefing Trump received:

LAUER: Did anything in that briefing, without going into specifics, shock or alarm you?
TRUMP: Yes. Very much so.
LAUER: Did you learn new things in that briefing?
TRUMP: First of all, I have great respect for the people that gave us the briefings. We — they were terrific people. They were experts on Iraq and Iran and different parts of — and Russia. But, yes, there was one thing that shocked me. And it just seems to me that what they said President Obama and Hillary Clinton and John Kerry, who is another total disaster, did exactly the opposite.
LAUER: Did you learn anything in that briefing — again, not going into specifics — that makes you reconsider some of the things you say you can accomplish, like defeating ISIS quickly?
TRUMP: No, I didn’t learn anything from that standpoint. What I did learn is that our leadership, Barack Obama, did not follow what our experts and our truly — when they call it intelligence, it’s there for a reason — what our experts said to do. And I was very, very surprised. In almost every instance. And I could tell you. I have pretty good with the body language. I could tell they were not happy. Our leaders did not follow what they were recommending.

First, the fact that Trump characterized what he was told in any way is a violation of the agreement he made to get those briefings. I can’t recall a single case of a presidential candidate doing that before. Ironically, this was an opportunity for Trump to act “presidential,” as he always says he can be. He could have just said, “I’m sorry, Matt, but I’m not at liberty to discuss what goes on in those briefings,” and it might have shown that he is taking them, and the responsibilities of the presidency more generally, with some modicum of seriousness.

Second, just as with his secret ISIS plan, I can’t prove beyond a shadow of a doubt that Trump is lying here, but he’s lying. If the briefers told him “what our experts said to do,” it would be unprecedented. And the idea that they communicated with their “body language” that they are unhappy with the administration’s decisions? Please.

Those briefings don’t have policy recommendations; they’re about informing the candidate about what’s going on in the world. That’s why people who actually know about this issue were positively gobsmacked by Trump’s comment. “I’ve covered intelligence and the intelligence community for a long time,” said NBC’s Andrea Mitchell. “I would be stunned that the CIA briefers signaled anything to Donald Trump” about their personal views on policy decisions.

I could cite many more examples from the forum, like Trump’s insistence on continuing to lie about whether he opposed the Iraq War from the beginning, or his ludicrous notion that what we should have done there is “take the oil,” as though it were standing stacked in barrels at a port waiting to be loaded onto our ships, and not lying underground in locations spread around the country. But here’s what’s so depressing about events like this one.

Our entire system is set up on the presumption that the people running for president will accept certain norms. Even if they might fib from time to time, they’ll agree that the truth does matter in a fundamental way, and that they’re accountable to it. They’ll accept that the presidency is a serious position and the people who would hold it should have some degree of understanding of the issues they’ll confront. They’ll accept that they have an obligation to explain what they’re going to do if they win. The campaign may be dominated by trivial controversies and superficial appeals, and both candidates are trying to put on a compelling show, but there has to be something substantive underneath that show, whether you agree with that candidate’s priorities or not.

Both parties’ nominees have always agreed on those basic norms. Yet Donald Trump accepts none of them. And right now he’s trailing Clinton by only around 5 points in the polls.