Donald Trump says his economic plans would save the government money and reduce the deficit. But in tonight's Fox News debate, moderator Chris Wallace made it perfectly clear that his numbers don't even begin to add up.

And Trump, insanely, continued to say that they do—and very nearly ended up insisting that he could cut $300 billion out of $78 billion in spending. Donald Trump's attempted defense of his plan was, instead, a demonstration of why it wouldn't work.

Wallace began by noting that Donald Trump's tax plan would increase the deficit* by a whopping $10 trillion, and that Trump generally dismisses this concern by saying that much of that could be made up by the elimination of waste, fraud, and abuse. So what, specifically, Wallace asked, would Trump cut?

Here's the relevant part of Trump's answer:

Department of Education. We're cutting Common Core. We're getting rid of Common Core. We're bringing education locally. Department of Environmental Protection. We are going to get rid are of it in almost every form. We're going to have little tidbits left but we're going to take a tremendous amount out. We have various other things. If you look at the IRS, if you look at every single agency, we can cut it down, and I mean really cut it down and save. The waste, fraud, and abuse is massive.

Okay, fine. Cut the Department of Education entirely. Eliminate the Environmental Protection Agency (we'll assume that's what he meant by "Department of Environmental Protection").

Even if you managed to completely cut all spending related to those entire departments, it still wouldn't even begin to eliminate the deficit we already have. As Wallace went on to note, this year's deficit alone is $544 billion. Trump's tax plan would add an additional $10 trillion in deficits over the next years. Wallace put this to Trump, telling him, "your numbers don't add up, sir."

Tellingly, Trump responded by shifting subjects and bringing up drug costs:

Let me explain something. Because of the fact that the pharmaceutical companies—because of the fact that the pharmaceutical companies are not mandated to bid properly, they have hundreds of billions of dollars in waste. We don't bid properly. We don't have proper bidding procedures. The reason we don't is because they take care of all of the senators, all of the congressman, and they don't bid. They don't go out to bid.

At which point Wallace pointed out that Trump's numbers—and there's no other way to put this—are complete and utter nonsense. Here's the full exchange, via The Washington Post's transcript:

TRUMP: Take a look—excuse me. You are talking about hundreds of billions of dollars… WALLACE: No, you are not. TRUMP: … if we went out to the proper bid. Of course you are. WALLACE: No, you're not, sir. Let's put up full screen number 2. You say that Medicare could save $300 billion a year negotiating lower drug prices. But Medicare total only spends $78 billion a year on drugs. Sir, that's the facts. You are talking about saving more money on Medicare prescription drugs… TRUMP: I'm saying saving through negotiation throughout the economy, you will save $300 billion a year. WALLACE: But that doesn't really cut the federal deficit. TRUMP: And that's a huge—of course it is. We are going to buy things for less money. Of course it is. That works out… WALLACE: That's the only money that we buy—the only drugs that we pay for is through Medicare. TRUMP: I'm not only talking about drugs, I'm talking about other things. We will save $300 billion a year if we properly negotiate. We don't do that. We don't negotiate. We don't negotiate anything.

So, to review, here is the structure of the exchange: Wallace asks Trump how he would offset the deficit increases incurred by his tax plan. Trump says waste, fraud, and abuse. Wallace asks Trump to be specific about cuts. Trump says he'd cut the Department of Education, and the EPA. Wallace says that even if you eliminate those programs entirely, it doesn't even come close to offsetting Trump's deficit increase. Trump doesn't respond directly, changes the subject, and brings up drug costs. Wallace points out that Trump's numbers on drug costs are also completely untethered from reality.

And then Trump insists—well, it's not totally clear what he ends up saying. But no matter what, it's absurd.

It's possible that he is just babbling incoherently, saying whatever random words come to mind. ("I'm not only talking about drugs, I'm talking about other things.") It's possible that he's trying to argue that when he claims $300 billion in savings, he's talking about savings throughout the economy. ("I'm saying saving through negotiation throughout the economy, you will save $300 billion a year.") But if that's the case, then that's an admission that the savings he promised from government spending are imaginary. And it's even possible that what he's trying to say is that he will cut $300 billion a year from $78 billion in Medicare prescription drug spending. (WALLACE: "But that doesn't really cut the federal deficit." TRUMP: "And that's a huge—of course it is.") Which would be…impressive, to say the least.

In any case, it's clear—not that it wasn't already—that Donald Trump has no idea what he's talking about when it comes to the budget, the deficit, health care policy, or, probably, anything at all. And when someone points this out, Trump's response, however you interpret it, is essentially to declare war on math, language, and reality itself.

(*Yes, this is really a way of saying that it would increase total debt by this much over the course of a decade, via annual increases in the deficit. But "deficits" has become the catch-all word for describing budget gaps, and that's how it was described in the debate, so for the purposes of this post, at least, that's the language I'm going to use.)