It is a mistake of historians and biographers to ascribe to a person one particular motive force, and then attribute every subsequent action of theirs to that personality trait. In politics, we compound this error by insisting that politicians act only or primarily because they want to get re-elected.

But boy, if persistent and deep insecurity doesn't push Donald Trump towards those microphones, I don't know what does. I don't think it's narcissism.

Now, of course we all suffer from imposter syndrome, which is the fear that our true level of capability will be exposed and our ability to BS our way out of tough situations will only get us so far.

But Trump has got it really bad.

1. He regularly and repeatedly insists that he is the most brilliant person, has the best memory, the greatest ideas; people who are relatively secure do not need to tell others that they are great, but people who are not secure have to cover a 10-foot gap with a 100-foot bridge, so afraid are they that what they actually have to say is exposing some fundamental flaw. Trump's use of superlatives belies a rather profound sadness. He desperately NEEDS you to know that he is right.

2. Forget about the financial braggadocio; Trump insists he's smart because he went to Wharton. He says this whenever someone questions his judgment. "I went to the Wharton School of Business. I'm, like, a really smart person," is one common formulation.

It's an axiom: When you have to cite your credentials, you're afraid that people are discounting them. Wharton is an Ivy; Trump earned his way into the school, at least partly; if he was truly stupid, even his father's reputation wouldn't have gotten him in all the way. So getting into Wharton represents something real that Trump accomplished (more or less) by himself. That's his first line of defense, mind you, when someone questions his ideas.

3. Sudden bursts of brashness. I get that Trump likes attention — we all do — and wants to be the loudest voice in the room — again, that's not abnormal — and that he understands how to manipulate news cycles. But there's a deeper reason for his instant recipe policies: He needs the approval of his crowds. It fortifies him against charges that he is empty, dumb, lucky, or a daddy's boy.

Very fortunately for Trump, a large number of his supporters validate him because they are hypersensitive to sleights against their own status and position in society right now. They're Christians under attack from secularists; Americans under attack from Muslims; conservatives under attack from their leadership in Congress; white people under attack from minorities; middle-class people under attack from poor people who are slurping up government services at their expense. Like Richard Nixon's "bundle of resentments" (Rick Perlstein's phrase), Trump's bundle of insecurities serve the interests of his potential voters right now.

These are just the macronutrients in Trump's brew. His penchant for insults — particularly physical insults — is not something that secure people do. Even mean, secure people do not gratuitously insult someone's appearance because they disagree with them. Mean, insecure people do because they instinctively know how powerful those insults can be, and how they can deflect attention from the flaws of the person who makes them.

Let me list a few other traits of powerful, insecure people:

1. They blurt out things told in confidence.

2. They constantly complain about being treated fairly.

3. They cannot account for anyone else's successes.

4. They surround themselves with sycophants who pantomime their method of relating to other people.

Donald Trump is just not very comfortable with being Donald Trump. His insecurity is not universal; he does not seem to be terribly obsessed with his hair, or his looks; he doesn't seem to care about being labeled a bigot or a racist. What he cares about is being seen as smart enough, as someone who worked hard to make it where he has made it.

And hey — he did go to Wharton.