The Fox News debate moderators brought slide decks showing budget stats and video clips showing flip-flops on Thursday — all meant to force Donald Trump to get specific about what he stands for and how he'll make good on his campaign promises. It was a valiant effort -- and it was all in vain.

We've said over and over that Trump defies all conventional rules of politics, but Thursday's Republican presidential debate in Detroit was an especially vivid example of his apparent immunity. He wriggled off every hook with blustery nonsense and turned conversations of national significance into frat-boy arguments with name-calling and an anatomy joke. The Fox Theater might as well have been the house of Phi Beta Trump.

Chris Wallace rightly earned praise for his live fact-checking of Trump's plan to reduce the federal deficit through shrewder negotiation and the elimination of "waste, fraud and abuse." At one point, the GOP front-runner repeated one of his favorite claims — that he'll save the country "hundreds of billions of dollars" by bargaining down pharmaceutical companies to lower drug prices. Wallace was ready for a decisive debunking.

WALLACE: 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.

What do you do with that? Wallace proved the mathematical impossibility of Trump's promise, so Trump instantly altered the promise to cover "other things." That's not a real answer. But does anyone doubt that his supporters will be satisfied by it?

Later, Megyn Kelly played a highlight reel of Trump's contradictory statements. The topics happened to be the invasions of Iraq and Afghanistan, and the acceptance of Syrian refugees, but she could have picked any number of subjects.

KELLY: The point I'm going for is you change your tune on so many things, and that has some people saying, "What is his core?"

TRUMP: Megyn, I have a very strong core.

(APPLAUSE)

I have a very strong core. But I've never seen a successful person who wasn't flexible, who didn't have a certain degree of flexibility. You have to have a certain degree of flexibility.

(APPLAUSE)

You can't — for instance, let's say, on — on the second question, you can't say it's OK, and then you find out it's not OK, and you don't want to do anything. You have to be flexible, because you learn.

So there. Strong core. Flexibility. Other words. Case closed.

This level of reasoning wouldn't fly in a grade-school book report, yet through sheer force of personality, Trump convinces many voters that his non-answers are actually the exact answers America needs. Journalists who highlight his vapidness — or try to push him into deeper water — are just haters.

The Fox moderators certainly deserve the accolades they're getting — and the kudos are indeed flowing in, even from people generally aren't Fox fans.

But let's just be realistic about the effectiveness of their attempts to pin down Trump. He simply refused to let it happen. And his backers will love him for it.