One of the comments that political observers offer to reporters with some regularity is that more should be done to challenge President Trump’s repeated lies and inaccuracies about matters of public policy. Given the regularity with which Trump offers disproved bits of data, it would seem to be a fairly trivial task to interject with corrections.

In practice, of course, it’s not that simple: The president’s availability is limited, and while he tends to repeat debunked talking points, the broad selection of inaccuracies from which he might choose on any given day means that reporters might not always be prepared for any particular comment.

On Friday, though, everything fell into place: The president, in trying to defend his decision to declare a national emergency to fund a wall on the border with Mexico, trotted out the same frequently disproved data he has been using since the fight over the wall heated up in December. And reporters, given the opportunity to ask questions of the president, directly challenged his presentation of facts.

In short order, we saw why trying to fact-check Trump, even in real time, is often an unrewarding enterprise. The combination of the power imbalance between the president and reporters, his willingness to ignore the decorum that has usually guided such interactions, and his aggressive lack of interest in engaging in legitimate debate all made the day’s incursions broadly unsuccessful.

CNN’s Jim Acosta

The first reporter to challenge Trump’s data was CNN’s Jim Acosta. Acosta’s tense relationship with the White House is by now well established, including an incident in which Acosta’s access badge to the facility was briefly revoked.

Here was their exchange, with our thoughts interspersed.

ACOSTA: Thank you, Mr. President. I — I wonder if you could comment on this disconnect that we seem to have in this country where you are presenting information about what’s happening at the border, calling it an invasion, talking about women with duct tape over their mouths and so on.

And yet there’s a lot of reporting out there, there’s a lot of crime data out there, there’s a lot of Department of Homeland Security data out there that shows border crossings at a near-record low …

TRUMP: That’s because of us. But it’s still — excuse me …

A problem with asking questions of anyone, Trump included, comes when you include multiple issues in one question. This, too, can stem from having only limited time to press the president on any given subject (and his press secretary’s abandonment of daily press briefings).

Here, Trump seizes upon one part of Acosta’s question — a drop in border crossings — to interrupt.

Trump’s claim that border crossings are near a record low is not because of Trump. Data on monthly apprehensions at the border, a good proxy for the number of crossings, shows that there was a low early in Trump’s administration, but the figure has since climbed. Apprehensions are now at a level that has been fairly consistent since 2011 or so.

ACOSTA: That shows undocumented immigrants committing crimes at lower levels …

TRUMP: It’s still massive numbers of crossings.

Acosta presses on as Trump pivots from taking credit for a drop in border crossings to instead touting how many crossings there are — the central argument behind his push for a wall.

Consider that contrast alone. Trump claims we need a wall to address a crisis at the border, but also accepts and seeks credit for the number of crossings being near a record low.

ACOSTA: Shows undocumented criminals — or undocumented immigrants committing crimes at lower levels than native-born Americans. What — what do you say to …

TRUMP: You don’t — you don’t really believe that stat, do you? Do you really believe that stat? Take a look at our federal prisons.

ACOSTA: What do you — well, let me ask you this. I believe — I believe in facts and statistics (inaudible).

TRUMP: Okay. Anymore? Quick, let’s go.

Acosta asks about a claim that Trump has made since he declared his candidacy: that immigrants from Mexico bring crime.

The idea that immigrants, including immigrants in the country illegally, commit a disproportionate amount of crime has been repeatedly shown to be false. It was false in July 2015 when Trump first made the claim, and, since Trump has focused on the issue, it has been again disproved repeatedly.

Trump doesn’t offer any factual response to Acosta, besides to point at the federal prison population. (Since immigration crimes are federal crimes, the federal prison population is disproportionately made up of non-citizens.) Trump simply asks Acosta what he believes, as though his own gut feeling is more important than what statistical analysis suggests.

That discrepancy comes up again in short order.

ACOSTA: Let me just ask you this: What do you say to your critics who say that you are creating a national emergency, that you’re concocting a national emergency here in order to get your wall because you couldn’t get it through other ways?

TRUMP: I ask the Angel Moms, what do you think? Do you think I’m creating something? Ask these incredible women who lost their daughters and their sons, okay? Because your question is a very political question, because you have an agenda, you’re CNN, you’re fake news, you have an agenda.

The numbers that you gave are wrong. Take a look at our federal prison population, see how many of them percentage-wise are illegal aliens, just see. Go ahead and see. It’s a fake question.

Acosta tries another tack: Isn’t this not an emergency but instead simply an effort to get the wall that Congress denied?

Trump demands that Acosta consider the “Angel Moms,” mothers of people who’ve lost children to immigrants in the country illegally either through criminal acts or accidents. This is another appeal to emotion, centered on undeniable tragedies — but tragedies that by themselves don’t prove Trump’s claims about the risk posed by immigrants in the country illegally. (Native-born Americans commit crimes at higher rates than immigrants.)

The president then switches to the point he probably wanted to make from the time he called on Acosta: CNN’s coverage can’t be trusted because it has an agenda.

It’s particularly ironic that Trump would make this claim after having just waved away pointed questions about issues of fact in favor of politically motivated emotion. But it’s not particularly surprising that he did so.

Playboy‘s Brian Karem

When Acosta was done, Trump turned to Playboy’s White House correspondent, Brian Karem. Karem continued Acosta’s theme.

KAREM: Thank you, Mr. President. Just to follow up on that, you — unifying crime-reporting statistics, numbers from your own Border Patrol, numbers from this government, show that the amount of illegal immigrants are down, there is not violence on the border and that most …

TRUMP: There’s not violence on the border?

KAREM: There’s not as much violence as — wait a minute — wait a minute — let me finish the question …

TRUMP: Oh really? You had 26 people killed?

KAREM: Please, let me finish the question, please.

TRUMP: Two weeks ago, 26 people were killed in a gunfight on the border.

KAREM: I understand what the — I understand what you’re saying.

TRUMP: A mile away from where I went.

KAREM: I — I was there, I understand. That’s not the question. The question is …

TRUMP: Do we forget about that?

Karem begins by noting that the number of immigrants in the country has declined and addressing the question of violence on the border. But he misspeaks, and Trump immediately pounces.

Nearly half of Karem’s time is taken up fending off Trump’s accusation that Karem was claiming there was no violence on the border. It’s an accusation that’s clearly not made in good faith, as Karem quickly makes clear, but Trump keeps pressing on it because it allows him to filibuster — and avoid the question.

KAREM: No, I’m not forgetting about it, I’m asking you to clarify where you get your numbers, because most of the [Drug Enforcement Administration] crime-reporting statistics that we see show that drugs are coming across at the ports of entry, that illegal immigration is down and that the violence is down. So what do you base your facts on?

TRUMP: Okay. Let me — come on, let’s go.

KAREM: And secondly …

TRUMP: No, no, you get one, you get one. Wait, sit down, sit down.

KAREM: Could you — could you please answer it.

TRUMP: Sit down! You get one question.

KAREM: Please?

TRUMP: I get my numbers from a lot of sources, like Homeland Security primarily, and the numbers that I have from Homeland Security are a disaster.

And you know what else is a disaster? The numbers that come out of Homeland Security, Kirstjen [Nielsen, the homeland security secretary], for the cost that we spend and the money that we lose because of illegal immigration, billions and billions of dollars a month. Billions and billions of dollars, and it’s unnecessary.

Karem finally gets back on track: Where, if Trump is claiming that there is a risk of crime at the border, does that analysis come from?

Primarily the Department of Homeland Security, Trump says — leaving open the door for other sources of information, including, perhaps, the conservative media that Trump eagerly consumes.

Mind you, Trump doesn’t offer any data on crime, instead asserting that Homeland Security estimates that illegal immigration costs billions of dollars a month.

Trump has made similar claims before, frequently inflating the annual cost of immigration on a whim. The Post’s fact-checkers have looked at Trump’s numbers in the past and determined that his claims derive indirectly from numbers tallied by a group that opposes current immigration policies. Even that analysis has been challenged as inaccurate.

In other words, this appears to be an example of one of the other sources of information, not DHS.

KAREM: So your own government’s stats are wrong, are you saying?

TRUMP: No, no, I use many stats. I use many stats.

KAREM: Could you share those stats with us?

TRUMP: Let me tell you, you have stats that are far worse than the ones that I use, but I use many stats, but I also use Homeland Security. All right, next question.

Karem returns to his point about the Drug Enforcement Administration’s determination that most drugs come into the United States at existing border checkpoints, a bit of information that’s reinforced by testimony from Homeland Security.

Trump’s reply? He uses lots of stats, ones that are better than what Karem has, but he won’t share them.

And with that, Karem’s turn with the mic was over. The next question was about China.

The takeaway here is simple: Trump is uninterested in presenting accurate information about immigration that conflicts with his policy goals. He prefers instead to go with his gut, even when those feelings are demonstrably false. And if you challenge him on that, he’ll bully and mislead and then cut you off.

Reporters should and do press Trump on his assertions of fact. But it will usually go like this.