One big difference between Trump and Hillary Clinton is that Clinton has been punished for shading the truth. Photograph by Eric Thayer / The New York Times / Redux

According to many accounts, it was the young Adolf Hitler who coined the term “Big Lie.” In his 1925 tract, “Mein Kampf,” he wrote that “the broad masses” are more likely to “fall victims to the big lie than the small lie,” because “It would never come into their heads to fabricate colossal untruths, and they would not believe that others could have the impudence to distort the truth so infamously.”

Contrary to some accounts, neither Hitler nor his propaganda minister, Joseph Goebbels, took credit for successfully using what the French refer to as le grand mensonge: the Nazi leaders always claimed they were telling the truth. In Hitler’s mind, it was the Jews of Vienna who spread the original Big Lie—about Germany’s conduct in the First World War. Goebbels later blamed the English, saying they “follow the principle that when one lies, one should lie big, and stick to it.”

Donald Trump, we can safely assume, hasn’t been studying the origin of the phrase. But for many months now he has been repeating a very sizable whopper: the claim that he opposed the Iraq War all along. He said it again on Wednesday night, aboard the U.S.S. Intrepid, where he appeared at a “Commander-in-Chief Forum” that was broadcast on NBC and MSNBC. “I was totally against the war in Iraq,” Trump told the moderator, Matt Lauer. “You can look at Esquire magazine from ’04. You can look at before that.”

Actually, plenty of people—journalists, fact-checkers, opposition researchers—have followed Trump’s advice, and what they have discovered is that there is no public record of him criticizing the war before it began. But there is a record of Trump saying he supported it. On September 11, 2002, he appeared on “The Howard Stern Show,” where the host asked him if he was “for invading Iraq.” Trump replied, “Yeah, I guess so. I wish the first time it was done correctly.” This wasn’t the most fulsome of endorsements, it is true. But it clearly indicated that Trump backed sending in troops to overthrow Saddam Hussein.

During Hillary Clinton’s appearance with Lauer on Wednesday, which took place just before Trump’s, she pointed to Trump’s statement to Stern, saying of her opponent, “He refuses to take responsibility for his support.” When it was Trump’s turn on the stage, he didn’t avoid the potentially embarrassing subject—he brought up Clinton’s claim about his own accord, and acted offended. “I was against the war in Iraq because I said it’s going to totally destabilize the Middle East, which it has,” he insisted.

Depending on how charitable one feels, Trump’s blatant disregard for the factual record could be described as chutzpah, self-delusion, or the default reaction of someone to whom lying has become, in the words of his ghostwriter Tony Schwartz, “second nature.” (“More than anyone else I have ever met, Trump has the ability to convince himself that whatever he is saying at any given moment is true, or sort of true, or at least ought to be true,” Schwartz told my colleague Jane Mayer.)

But Trump isn’t just a master of the Big Lie. He’s adept at trotting out small and medium-sized stretchers, too. At one point Wednesday night, Lauer asked him whether he had heard anything in his two recent intelligence briefings that had prompted him to reconsider any of his policies. “No, I didn’t learn anything from that standpoint,” Trump replied. “What I did learn is that our leadership, Barack Obama, did not follow what our experts and our truly—when they call it intelligence, it’s there for a reason—what our experts said to do.”

For some reason, Lauer tried to move on to take a question from the audience, but Trump wasn’t finished. “And I was very, very surprised,” he went on. “In almost every instance. And I could tell you. I have pretty good with the body language. I could tell they were not happy. Our leaders did not follow what they were recommending.”

To be sure, we can’t know exactly what the briefers said to Trump, or how they expressed themselves. But does it seem in any way conceivable that the career intelligence officers who carried out the briefing would have indicated that the President and other senior officials had failed to follow their advice? It does not. Intelligence briefers don’t give advice; they present information that has been gathered through various channels. As Leon Panetta, the former head of the C.I.A., pointed out afterward on MSNBC, it would be a serious violation of their responsibilities to act in the way Trump indicated.

We will see if Trump repeats this new outlandish claim in the coming days. Until he does, it could probably be categorized, by his demanding standards, as a medium lie, rather than a big one. It is the sort of thing he throws out every so often—a bit like his claims that President Obama founded ISIS, or that “thousands and thousands” of people in Jersey City cheered the collapse of the Twin Towers. Trump must know such things didn’t happen. But, in his world, the truth’s value is instrumental, rather than intrinsic. “He lied strategically,” Schwartz told Mayer. “He had a complete lack of conscience about it.” (Last week, The New Yorker launched a new series of reported essays about Trump’s relationship with the truth.)

Clinton, of course, has also made some statements in the past that have turned out to be incomplete or downright false. At the start of the forum, Lauer spent quite a lot of time grilling Clinton about her private e-mail server, and whether she had mishandled classified information, subjects on which Clinton’s language has, shall we say, evolved. She insisted that none of the e-mails she sent or received as Secretary of State had a proper classified header. But she didn’t point out—as the Washington Post’s Fact Checker column did—that, according to James Comey, the director of the F.B.I., three e-mails sent to her server bore the marking “(c),” which stood for “confidential.”

One big difference between Trump and Clinton is that Clinton has been punished for shading the truth. Comey issued an unprecedented public rebuke to her, and public surveys testify that most Americans now think of her as untrustworthy. If Clinton were to lose in November, the e-mail story would be a big factor in her defeat.

Trump, on the other hand, is the beneficiary of a double standard. When he utters some outrageous falsehood, as he does almost every day, the reaction in some quarters is that it is just Trump being Trump. He’s the P. T. Barnum of the modern age, and he’s been telling stretchers for decades. What else can you expect?

But this isn’t Trump being Trump. This is Trump running for President, and, according to the latest polls, he’s within a few points of the lead. It’s time to call him out for what he is: a compulsive liar.