Many Americans complain that Donald Trump has a tiny vocabulary. But he disproved his critics Wednesday during an impromptu press conference on the South Lawn of the White House.

In the past, Trump has repeatedly reminded people about his keen intellect by insisting “I’m smart.” Wednesday, he dug deep into his massive personal word bank and uttered a five-word sentence, “I’m a very intelligent person.”

Not only is that sentence three words longer than “I’m smart,” it is also three words longer than the phrase “f**king moron,” which is what his Secretary of State Rex Tillerson allegedly called him not long ago.

Wednesday’s boast came in response to a reporter who asked Trump if he should be more civil.

“Well I think the press makes me more uncivil than I am,” the president said, and then quickly switched the topic from his manners to his mind.

“You know, people don’t understand, I went to an Ivy League college. I was a nice student. I did very well. I’m a very intelligent person.”

Even long before he started running for president, Trump repeatedly claimed that he’s both well-educated and brainy. Each time, it isn’t clear if he’s trying to convince his interviewers or himself.

In a 2004 interview with CNN, Trump said, “I went to the Wharton School of Finance. I got very good marks. I was a good student. It’s the best business school in the world, as far as I’m concerned.”

In 2011, in an interview with ABC, Trump said, “Let me tell you, I’m a really smart guy. I was a really good student at the best school in the country,” referring once again to Wharton, the University of Pennsylvania’s business school, where he earned a bachelor’s degree in 1968.

“I went to the Wharton School of Finance,” he said during a speech in Phoenix in July 2015, a month after announcing he was running for president. “I’m, like, a really smart person.”

The next month, in an interview on NBC’s “Meet the Press,” Trump described Wharton as “probably the hardest there is to get into.” He added, “Some of the great business minds in the world have gone to Wharton.” He also observed: “Look, if I were a liberal Democrat, people would say I’m the super genius of all time. The super genius of all time.”

During a CNN-sponsored Republican town hall in Columbia, South Carolina, in February 2016, Trump reminded the audience that he had gone to Wharton and repeated the same boast: “Look, I went to the best school, I was a good student and all of this stuff. I mean, I’m a smart person.”

Even after winning the White House, Trump couldn’t help reminding people about his mental muscles. He did it a few days after his inauguration during a visit to CIA headquarters. Trump’s handlers staged the event so he could demonstrate his full support for the agency (despite having spent much of his campaign bashing the nation’s intelligence community) and to divert media attention away from the 750,000 Americans who had come to Washington, D.C., that day to protest Trump’s presidency. But Trump’s scripted remarks turned into an impulsive rambling rant that included attacks on the media and his insistence that as many as 1.5 million people attended his inauguration (despite photos revealing no more than 250,000).

In the middle of his tirade, Trump felt the need to tell the nation’s top spies that he was a bright guy.

“Trust me,” Trump said. “I’m, like, a smart person.”

Last December, Trump repeated those same words while explaining why he intended to be the first president since Harry Truman to avoid getting daily updates from intelligence professionals about national security threats.

“I’m, like, a smart person,” he told Fox News’ Chris Wallace.

Anyone who feels compelled to boast how smart he is clearly suffers from a profound insecurity about his intelligence and accomplishments. In Trump’s case, he has good reason to have doubts.

Trump has the kind of street smarts (what he’s called “gut instinct”) characteristic of con artists and hucksters, but his limited vocabulary, short attention span, ignorance of policy specifics, indifference to scientific evidence, and admitted aversion to reading raise questions about his intellectual abilities—his capacity to absorb and analyze information and ideas.

Many observers have noted that Trump has a difficult time expressing himself and speaking in complete sentences. A linguistic analysis by Politico found that Trump speaks at a fourth-grade level. A study by researchers at Carnegie-Mellon University compared last year’s Republican and Democratic presidential candidates in terms of their vocabulary and grammar. Trump scored at a fifth-grade level, the lowest of all the candidates.

Some might suspect that this is not an intellectual shortcoming, but instead Trump’s calculated way of communicating with a wide audience. But Tony Schwartz, who spent a great deal of time with Trump while ghostwriting his 1987 book The Art of the Deal, noted that Trump has a very limited vocabulary. It would hardly be surprising if these observations infuriated the vain and insecure Trump.

Trump’s persistent insults directed toward anyone who disagrees with him also suggest his deep insecurity. Trump has constantly denigrated his opponents and detractors as “losers,” among them actresses Rosie O’Donnell, Cher, and Meryl Streep, civil rights icon John Lewis, businessman Mark Cuban, GOP political operatives Karl Rove and Ana Navarro, NBC’s Chuck Todd, Jeb Bush, Weekly Standard editor Bill Kristol and conservative columnist George Will.

It turns out that loser is one of Trump’s favorite words. An archive of Trump’s Twitter account reveals that between 2009 and his January 2017 inauguration he used the word “loser” 234 times. His other favorite insults included “dumb” or “dummy” (222 tweets), “terrible” (202), “stupid” (182), “weak” (154) and “dope” (115).

On May 8, 2013, at 6:37pm, Trump tweeted: “Sorry losers and haters, but my I.Q. is one of the highest -and you all know it! Please don’t feel so stupid or insecure, it’s not your fault.”

At 3:52 pm on Sept. 26, 2014—nine months before he announced his candidacy for the White House—Trump tweeted: “I wonder if I run for PRESIDENT, will the haters and losers vote for me knowing that I will MAKE AMERICA GREAT AGAIN? I say they will!”

On September 17, 2016—after CNN anchors criticized Trump for promising a “big announcement” to get the media to come to an event, only to use the moment to tout his new hotel and then invite several military figures onstage to praise him—Trump had another Twitter tantrum at 8:13am: “CNN just doesn’t get it, and that’s why their ratings are so low – and getting worse. Boring anti-Trump panelists, mostly losers.”

Trump sometimes uses other words to convey the same thought (he recently called Tennessee Senator Bob Corker a “lightweight”), but his insults all seek to demean his critics in order to boost his own ego. Whether he’s attacking Republican Senator Jeff Flake of Arizona or San Juan’s Democratic Mayor Carmen Yulín Cruz, Trump views the world in zero-sum terms, as if there were a finite number of IQ points.

Truly smart people don’t have to constantly boast about how smart they are. Only someone who doubts his own intelligence would feel compelled to make these kinds of public statements.

Trump surely knows he didn’t get into Wharton on his own merits. He transferred into the University of Pennsylvania’s undergraduate program after spending two years at Fordham University in New York, where he had no significant achievements.

“No one I know of has said ‘I remember Donald Trump,’” Paul F. Gerken, a 1968 Fordham graduate and president of the Fordham College Alumni Association, told the Chronicle of Higher Education. “Whatever he did at Fordham, he didn’t leave footprints.”

According to Gwenda Blair’s 2001 biography, The Trumps, Trump’s grades at Fordham were not good enough to qualify him for a transfer to Wharton. Blair wrote that Trump got into Wharton as a special favor from a “friendly” admissions officer who knew Trump’s older brother, Freddy. The college’s admissions staff surely knew that Trump’s father was a wealthy real estate developer and a potential donor. Other than his father’s money and his family’s connections, Trump had no qualifications that would have otherwise gotten him into Wharton. (Most people who mention Wharton refer to its prestigious MBA program, but Trump was an economics major in the undergraduate program.)

Moreover, Trump has for years exaggerated his academic accomplishments at Penn.

On at least two occasions in the 1970s, the New York Times reported that Trump “graduated first in his class” at Wharton in 1968. That’s not true. The dean’s list for his graduation year, published in the Daily Pennsylvanian, the campus newspaper, doesn’t include Trump’s name. He has refused to release his grade transcripts from his college days.

It is likely that Trump was the original source for that falsehood, but it isn’t entirely clear, since neither Times article attributes it directly to him. But the fabrication that Trump was first in his class has been repeated in many other articles as well as books about Trump, so he clearly knew it was out there in the public domain and has never bothered to correct it.

“He was not in any kind of leadership. I certainly doubt he was the smartest guy in the class,” Steve Perelman, a classmate of Trump’s at Wharton, told the Daily Pennsylvanian in 2015.

Upon graduating from college, Trump didn’t have to apply for jobs or go through interviews with potential employers who would judge him on his merits. Instead, his father Fred Trump handed young Donald the keys to his real estate empire. Trump’s insecurity about his accomplishments is also revealed in his efforts to portray himself as an up-by-the-bootstraps self-made entrepreneur.

“It has not been easy for me,” Trump said at a town hall meeting on October 26, 2015, acknowledging, “My father gave me a small loan of a million dollars.”

At a news conference last year, Trump repeated the same story: “I got a very, very small loan from my father many years ago. I built that into a massive empire and I paid my father back that loan.”

An investigation by the Washington Post in March 2016 demolished Trump’s claim that he made it on his own. Not only did Trump’s multi-millionaire father provide Donald with a huge inheritance, and set up big-bucks trust accounts to provide his son with a steady income, Fred was also a silent partner in Trump’s first real estate projects. According to the Post:

“Trump’s father—whose name had been besmirched in New York real estate circles after investigations into windfall profits and other abuses in his real estate projects—was an essential silent partner in Trump’s initiative. In effect, the son was the front man, relying on his father’s connections and wealth, while his father stood silently in the background to avoid drawing attention to himself.”

Fred Trump’s real estate fortune was hardly due to his faith in the free market, but instead stemmed from his reliance on government subsidies. He made his money building middle-class apartments financed by the Federal Housing Administration.

In 1954, when Donald was 8 years old, his father was subpoenaed to testify before the Senate Banking Committee on allegations that he had ripped off the government to reap windfall profits through his FHA-insured housing developments. At the hearings, the elder Trump was called on the carpet for profiteering off public contracts, including overestimating the construction costs of his projects in order to get larger mortgages from FHA. Under oath, he reluctantly admitted that he had wildly overstated the development costs.

Donald has followed in his father’s corrupt footsteps. Trump’s career is littered with bogus businesses (like Trump University); repeated ripoffs of suppliers, contractors and employees whom he failed to pay for services rendered; and the misuse of the Trump Foundation to feather his own nest while trying to look like a philanthropist. Six of Trump’s businesses have gone bankrupt.

Despite this, on April 18, 2015, Trump tweeted this falsehood: ”For all of the haters and losers out there sorry, I never went Bankrupt.”

Trump has also lied about the size of his wealth, as various business publications have pointed out. Many observers suggest that one reason Trump has refused to release his tax returns is that they will show that he has repeatedly and wildly exaggerated his wealth and thus his success.

Embarrassed by his lackluster academic record, his dependence on his family’s connections and wealth to get into college and to succeed in business, and his troublesome and abusive business practices, Trump lashes out at anyone who challenges him, no matter how insignificant the matter.

Many observers have noted Trump’s sociopathic, thin-skinned, demagogic, authoritarian, impulsive, and vindictive personality. Although Trump has the self-awareness of an adolescent, it is obvious to many others that his compulsion to constantly boast “I’m smart” and to deride others as “losers” is rooted in his profound sense of insecurity.

Presidents don’t have to be geniuses. But a successful president must recognize his own limitations and be willing to rely on others’ expertise. He has to take constant criticism—from the media, political opponents, and his own advisers—without taking it too personally. Surrounding oneself with yes-men and -women who are afraid to tell the president he’s wrong is a recipe for disaster. Most important, an effective president needs good judgment—to be able to hear different viewpoints, weigh evidence, think several steps in advance rather than act impulsively, and be calm under intense pressure. Trump fails each of these tests.

Beneath Trump’s public bravado is a deeply insecure, troubled man who is unfit to be president. This makes him a danger to the country and the world.