Near the end of a Wednesday-morning interview in which he tried (unsuccessfully) over and over to get an admission of plagiarism, CNN's Chris Cuomo decided to be very blunt with Donald Trump's campaign chairman, Paul Manafort.

"I can't move on because you keep lying," Cuomo said.

There are two big things to unpack in one little retort. One is Cuomo's relentlessness on the subject of plagiarized material in Melania Trump's address to the Republican National Convention Monday night; the other is his use of the "L" word — lying.

Cuomo explained the first on his own:

A big part of the case I'm hearing here at the convention for why Donald Trump needs to be president is that Hillary Clinton can't be trusted, that she doesn't level with the American people, which is another way of saying she lies. That is what this is going on right now with this issue that should be small about this speech.
You don't like that you got caught with some of Michelle Obama's language in the speech. Who knows how it happened? You had a big group working with Melania, don't want to acknowledge it because that's the way this campaign works.
That plays into the second problem, which is that when faced with something that you did wrong, you just deny it, no matter whether it's true or not. Whether it's the man who has a developmental disability who works for the New York Times, and Donald Trump mocks him and then says, no, I didn't. Whether it's a star that represents the Star of David and you say, no, it's a sheriff's star.
There is a pattern, whether it's Baron, John Miller, that was really Donald Trump. There's a pattern of denying the obvious. What happens when you're running the government of the United States, and you don't want to deal with what happens then? That's the concern. That's why I don't understand you won't just own this little thing and move on.

Well said. The Trump campaign's refusal to admit obvious plagiarism undermines the Republican presidential nominee's credibility, as he attacks Clinton for dishonesty. And Trump's general unwillingness to acknowledge mistakes raises questions about how he would handle missteps as president. That's why a seemingly small issue like borrowing language from a Michelle Obama speech matters in the election — and why Cuomo and the rest of the press won't just let it go.

Cuomo's unvarnished assertion that Manafort "keep[s] lying" matters, too, because mainstream journalists have been so reluctant to attach variations of the word "lie" to the Trump campaign. Reporters have mostly stuck with less-loaded terms such as "factual inaccuracies," or "false statements." Word choice is significant because "lie" suggests intent; calling a statement "false" or "inaccurate" leaves open the possibility that the speaker got it wrong but didn't mean to.

The Fix's Philip Bump elaborated on this idea last fall when he explained "why the media won't say Donald Trump is lying":

The problem that arises is that we can't know his intentionality. Unless Trump comes out and says something equivalent to, "I was trying to deceive people," we can't say with certainty that this was his intention — no matter how obvious it may seem and no matter how many times in the past we've wondered about his intentionality. One time, the boy who cried wolf actually saw wolves.

So that's why reporters usually don't say Trump or his aides are "lying," even if it seems clear that they are. But Cuomo set aside such prudence, apparently certain that Manafort intended to deceive viewers about plagiarized sections of Melania Trump's speech.

The question is whether this is a one-time thing or a sign that journalists are getting bolder as Trump — now officially the GOP nominee — barrels on toward Election Day.