ASSOCIATED PRESS Republican presidential nominee Donald Trump amps up his attacks on Democratic rival Hillary Clinton as a "liar" at a New Hampshire rally Saturday. Some historians, though, see Trump as the most dishonest presidential candidate in American history.

WASHINGTON – Win or lose this November, Donald Trump is headed for the record books regardless, presidential historians say, albeit with an admittedly dubious achievement: the most falsehood-prone candidate in the two centuries of the republic.

“In American history, we’ve never had a major presidential candidate who fabricated facts with the regularity of Donald Trump,” said Douglas Brinkley, a history professor at Rice University. “He just simply makes up things.”

In the span of a few days last week, Trump falsely claimed that the NFL had sent him a letter complaining about this autumn’s debate schedule, when in fact it had not. He claimed that the Koch brothers had tried to meet with him about offering their support, when in reality they had no interest in doing so. And, most astonishingly, he claimed he had seen a video showing hundreds of millions of dollars being unloaded from a plane in Iran, fabricating embellishments about the video’s provenance, even after his campaign conceded that no such video existed.

Theda Skocpol, a government and sociology professor at Harvard, agreed that Trump’s dishonesties have set a new standard. “Trump lies constantly and shamelessly. I do think he is in new territory,” she said.

GOP leaders trying to attack Democratic nominee Hillary Clinton over her problems with honesty, meanwhile, are growing increasingly frustrated with their own candidate’s near-daily false statements. “What can I say? We nominated a fabulist,” said one top Republican official privately. “There’s no defending that.”

Trump’s willingness to say things that are provably untrue, of course, is not something that began with his campaign. The 70-year-old has been known for his exaggerations and outright fabrications for decades.

When he bought the Eastern Airlines Washington-to-New York shuttle in 1989 and renamed it Trump Airlines, he claimed, without any facts, that the other carrier operating that route did not maintain its planes as well as he did.

Throughout the 1990s and 2000s, he claimed stakes in properties in which he had no ownership interest, but was merely licensing the use of his name or was in line to collect a percentage of future profits. When confronted by lawyers in a 2007 deposition about this, he at first insisted that he was correct, but then replied that not having ownership was actually smarter because it was not possible for him to lose any money should the investment tank.

In 1991, at the age of 45, he invented a pseudonym for himself, called a gossip columnist and told her that “his boss,” Donald Trump, was dating Italian model Carla Bruni, when in fact he’d met her only once, a year earlier.

Last summer, in the early stages of his campaign, he told a Rolling Stone reporter riding aboard his private jetliner that it was larger than Air Force One – even though his Boeing 757 is nowhere near the size of the modified 747 used by the president.

And this spring – still stinging from former GOP nominee Mitt Romney’s speech ridiculing his various failed branded businesses – Trump pointed to a table of raw steaks and declared them “Trump Steaks,” even though that product has not been available for close to a decade.

A Republican consultant close to the Trump campaign, who also spoke on condition of anonymity, said Trump’s behavior is typical among wealthy candidates he has worked with.

“All those years in public life, nobody cared about the veracity of statements they made outside their business, which is the only place truth matters to them,” the consultant said. “Many people ― close staff, family ― let him go on about things for years and just roll their eyes, some afraid to say, ‘Stop it.’ Because it’s a sideshow, doesn’t matter. Then, suddenly, it matters. But the habit is there, set in stone.”

Falsehoods For The Sake Of Falsehoods

In Trump’s case, whether the word “lie” technically describes his falsehoods is unclear. By definition, “lying” means knowingly and purposefully misrepresenting facts. In Trump’s case, he often appears not to understand the difference between what he is saying and actual reality.

“I can’t think of any presidential candidate, Republican or Democrat, in recent American history who wasn’t accused of lying. It’s the nature of the job, almost, to skew facts toward a political end,” said University of Memphis historian Aram Goudsouzian. “But Trump lies more frequently, and on a larger scale. Most important, even when confronted with contrary evidence, he still insists that he is right. It is a special kind of delusion.”

“There have been candidates who embellished reality. Ronald Reagan sometimes remembered things that he actually remembered from a movie,” Rice University’s Brinkley said. “Nixon lied on purpose. He was lying to advance an idea forward. Donald Trump doesn’t even know he’s doing it, it’s so much part of his modus operandi.”

He added: “There’s something psychologically warped with someone who sees no distinction between facts and fiction at all. The sign of crazy is when someone believes his own bullshit. And he believes his own B.S.: Everything he says is true because he said it.”

Reagan’s confusion, as it turned out, may have been an early symptom of the Alzheimer’s diagnosis that was revealed in 1994, nearly six years after he left the White House.

If Trump is afflicted with any form of dementia, though, it’s something that has been going on for quite some time. In 2006, at age 60, Trump held a fundraiser for Florida’s Charlie Crist, then running for governor as a Republican, at his Mar-a-Lago resort in Palm Beach. Trump spoke for close to 45 minutes, talking about all the redecorating he had undertaken to the various rooms there, about his reality TV program, about all sorts of things related to Trump ― but said nothing about Crist. The candidate, in fact, was not even offered the opportunity to speak.

Trump’s need to invent facts about his own success appears to be a trait associated with narcissistic personality disorder, according to mental health professionals who have studied his public remarks, with the possibility that the malady may be antisocial personality disorder ― formerly known as sociopathy.

That certainly was the assessment of Texas Sen. Ted Cruz (R), who, on the day he lost the critical Indiana primary in May, lashed out at Trump’s relationship with facts. “This man is a pathological liar. He doesn’t know the difference between truth and lies,” Cruz said. “I say pathological because I actually think Donald, if you hooked him up to a lie detector test, he could say one thing in the morning, one thing at noon and one thing in the evening, all contradictory. And he’d pass the lie detector test each time. Whatever lie he’s telling, at that minute he believes it.”

Whether Trump’s behavior is actually a sign of mental illness is something only a professional assessment could determine, and it’s unknown whether Trump has ever sought one. His campaign did not respond to queries, and the physician who wrote a letter attesting to Trump’s health ― which closed with the line: “If elected, Mr. Trump, I can state unequivocally, will be the healthiest individual ever elected to the presidency” ― declined to speak to The Huffington Post.

Clinton’s Honesty Harder To Challenge With Trump

Whatever the reason behind Trump’s falsehoods, they have complicated the Republican Party’s efforts to use Clinton’s low scores for honesty and trustworthiness against her.

For 25 years, Republicans have characterized both former President Bill Clinton and Hillary Clinton as fundamentally dishonest, and the party has been working to make that case against her presidential campaign since it began last year.

Even as Clinton prepared to accept the nomination last month in Philadelphia, the RNC staged a news conference that afternoon accusing her of lying. “Deception and dishonesty are all second nature to Hillary,” said Arkansas Attorney General Leslie Rutledge. “Hillary will lie even when the truth would serve her better.”

But, later, Rutledge seemed at a loss to explain Trump’s falsehoods. “I’m not saying that Donald Trump ― everything he has said, I would advise him to say,” she said.

Indeed, an analysis by PolitiFact showed Trump scoring the worst among the major party candidates running for president this election, with 77 percent of his checked statements rated as false. Clinton, in contrast, had 28 percent rated false.

Andy Puzder, a top fundraiser for Trump and chairman of the company that owns the Hardee’s restaurant chain, said the comparison was not fair, as Clinton’s dishonesties were worse. Her 2008 statement that her airplane had come under sniper fire upon landing in Bosnia a dozen years earlier, her blaming the 2012 Benghazi terrorist attacks on an anti-Muslim YouTube video, and her much-criticized claims about her use of a private server for her government emails, Puzder said, were far more serious than Trump’s falsehoods.

“These are large and material things, and they matter,” he said.

But Shawn Steel, an RNC member from California and another fundraiser for Trump, conceded that Trump’s willingness to lie made it much harder for his side to attack Clinton on that front. “Any of the other 16 candidates would have had a much easier time of it,” he said, adding that it didn’t help that Trump’s falsehoods were so obvious and easily refuted. “She’s a far better liar. The quality of a lie from Hillary is on a much more sophisticated level.”

And the GOP consultant worried that Trump will be unable to control what’s become part of his lifestyle. “Truth hasn’t mattered for decades, so when it does matter it’s too late to change bad habits,” the consultant said.

Editor’s note: Donald Trump regularly incites political violence and is a serial liar, rampant xenophobe, racist, misogynist and birther who has repeatedly pledged to ban all Muslims ― 1.6 billion members of an entire religion ― from entering the U.S.