The 2016 election has been defined by Hillary Clinton's performance in the three presidential debates. Snap polls indicated she defeated Donald Trump in each encounter. And since the first debate, Clinton's lead over Trump has expanded both in terms of estimates of the popular vote and share of the Electoral College. Clinton's decisive victory was due to her talent and preparation. Trump lost because of obvious defects.

Trump can't maintain focus for 90 minutes. Particularly in the first and third debate, Trump began normally and then decompensated. Trump lost his composure, grew angry, interrupted Clinton, and blurted insults -- "such a nasty woman." As time passed, his remarks began to ramble and he often lost his line of reasoning. (In the third debate, Trump's response to his first question -- on the Supreme Court -- was to the point; after 90 minutes, his response to his last question --entitlements -- was incoherent.)

Some say that Trump -- who has made Clinton's health a campaign issue -- has his own health issue: stamina. Trump brags that he only sleeps three or four hours each night. Perhaps his stamina problem is due to sleep deprivation. Writing in the New York Times Timothy Egan argued that lack of sleep explains Trump's behavior, in general: "Sleep deprivation, we know, can make you cranky and temperamental, and throw off judgment. The severely sleep-deprived are more impulsive, less adaptable and prone to snappish decisions, and they have trouble listening to others."

My favorite psychologist argues that Trump's debate performance is actually a consequence of his narcissistic personality disorder. The psychologist observed that during each debate, Clinton was able to get under Trump's skin, to attack his fragile self-esteem with a series of barbs.

At the 24-minute mark of the third debate, Clinton clearly unhinged Trump with a remark about immigration: "[Donald] went to Mexico, he had a meeting with the Mexican president. Didn't even raise [the idea of a border wall]. He choked..." At that point, Trump decompensated: he became visibly angry and started to insult and interrupt Clinton. As a consequence, Trump's responses to questions became increasingly incoherent: At the one hour mark, Trump was asked what he would do as President after Mosul falls: "Will you put U.S. troops into that vacuum to make sure that ISIS doesn't come back?" Trump never answered the question. First he argued that the Mosul invasion had been timed to help Clinton and then that it would help Iran.

Trump did not adequately prepare for the debates. After the third debate, speaking at the Al Smith dinner, Clinton joked: "Donald wanted me drug tested before last night's debate. And look, I've got to tell you, I am so flattered that Donald thought I used some sort of performance enhancer. Now, actually, I did. It's called preparation."

In September, before the first debate, The New York Times reported that Trump's preparation was unorthodox: "[Trump] prefers not to do a full-length mock debate, and has no set person playing Mrs. Clinton. He is not using a lectern for mock debate drills... Some Trump advisers are concerned that he underestimates the difficulty of standing still, talking pointedly and listening sharply for 90 minutes. In the primary debates he often receded into the background, and only jumped into the debate forcefully when he was attacked. Some advisers worry that if Mrs. Clinton surprises him, he will be caught flat-footed." Trump's advisers warned him what might happen during the debates but he did not listen to them.

At the 26-minute mark of the third debate, Clinton observed: "[Donald] used undocumented labor to build the Trump Tower. He underpaid undocumented workers, and when they complained, he basically said what a lot of employers do: 'You complain, I'll get you deported.'" By this time Trump had decompensated and (amazingly) had no response.

At the 27-minute mark, Clinton asked: "Will Donald Trump admit and condemn that the Russians are [hacking] and make it clear that he will not have the help of Putin in in this election, that he rejects Russian espionage against Americans, which he actually encouraged in the past?" Trump equivocated, mumbling Putin "has no respect" for Hillary. She replied, "That's because he'd rather have a puppet as president of the United States." Trump childishly responded, "You're the puppet!"

Media consultant, Joel Silberman observed: "The first 30 minutes of the debate suggested that Republican presidential nominee Donald Trump had actually accepted coaching and was trying to practice self-control. Yet, from the beginning, I was struck by his nervous tics, his inability to stand still, his grabbing the microphone, his tight slit eyes, and his turned down mouth... by minute 30, he appeared physically unlikable... Mr. Trump's body and face language was both defensive and bullying."

In the debates, Clinton needled Trump and he decompensated. There was nothing that Clinton said that Trump could not have anticipated -- tax returns, problems with women, friendship with Putin, etc. If Trump had taken the time to adequately prepare -- Clinton typically took four full days -- then he could have controlled his narcissism and prevented his decompensation.

Trump chose to not fully prepare for the debates. That's no surprise. One of the symptoms of narcissistic personality disorder is "exaggerating your achievements and talents." Trump often brags about how smart he is.

Before each debate, Donald Trump believed he needed only minimal preparation because he was inherently more talented that Hillary Clinton. The debate results proved otherwise. Trump lost because of his defects.