As of this week, Rep. Seth Moulton (D-Mass.) is running for president. That’s probably news to you, given that being one of the least well-known entrants into an already overflowing presidential field is not the sort of thing that tends to seize the national imagination. We note it here, though, not to inform you about his candidacy but to highlight something he said as a newly minted presidential candidate.

“Of course he’s a liar,” Moulton said of President Trump during a campaign stop in New Hampshire on Tuesday. “I think everybody knows he’s a liar. Some people are willing to forgive it. But we should not have to have that question. We should never have to question whether the commander in chief is telling the truth.”

This is a somewhat unusual comment for a politician to make. Not the part about Trump being dishonest; that’s well established. The Washington Post’s fact-checking team has identified more than 9,000 instances in which Trump has said something false or misleading just since he took office.

Those false claims really spiked around the time of the midterm elections, which bodes poorly for the next 18 months.

What’s somewhat unusual about Moulton’s comment is that there still exists an idea in some circles that simply pointing out Trump’s falsehoods should be sufficient to sway public opinion on him and his presidency. That perhaps Americans aren’t familiar with Trump’s track record and, once they learn about it, they will suddenly sour on him.

There are a few problems with that theory, but Moulton hit upon the most important one: Most Americans already see Trump as dishonest. In fact, since Trump announced his candidacy in June 2015, a majority of Americans have always said that they don’t believe Trump is honest or trustworthy.

That, as you may know, didn’t prevent Trump from being elected president. In part, that’s because he was running against Hillary Clinton, a candidate who was also seen as untrustworthy. (A November 2016 Post-ABC poll found about as many Americans said they thought Trump was more honest than Clinton than vice versa.)

Of course, the belief that Trump is dishonest is not uniform. Democrats and independents are much more likely to hold that position than Republicans are.

That’s a central problem in the idea that simply pointing out Trump’s dishonest comments will change opinions of him. Republican views of Trump’s honesty have been relatively steady since the election, as has been Republican approval of Trump.

One reason is that Republicans are more likely than most Americans to accept Trump’s false statements as true. In December, we ran an experiment, asking poll respondents to identify which of 11 pairs of statements was true: One made by Trump and one that reflected reality.

On average, people believed Trump’s false statements about a quarter of the time. Democrats did so slightly less often than that. Among Republicans, respondents believed Trump’s presentation over reality a third of the time. Trump’s strongest supporters believed his claim over reality slightly less than half of the time.

In our most recent poll, completed in January, 80 percent of Republicans said they viewed Trump as honest and trustworthy. This is probably in part a function of a willingness to cut Trump slack in ways that his critics are loath to do. It seems, in part, to also be a function of being more likely to accept even Trump’s false statements as true.

But from a political standpoint, these data undermine the idea that shining more light on Trump’s inaccuracies will erode his support. We at The Post and we in the media have been shining that light since he first declared his candidacy. After an initial surge in support from Republicans, views of Trump haven’t budged much. He has about as much support as he always did, and Americans are about as likely to view him as honest as they ever were.

Presidential candidate Seth Moulton is correct about what most Americans think. Those people who are willing to forgive Trump’s falsehoods, as he puts it, are also people who almost certainly would not vote for Seth Moulton for president.