Dean Obeidallah, a former attorney, is the host of SiriusXM's weekly program "The Dean Obeidallah Show," a columnist for The Daily Beast and editor of the politics blog The Dean's Report . Follow him @TheDeansreport . The opinions expressed in this commentary are his.

(CNN) If you're waiting for Donald Trump to pivot to become "presidential" -- a candidate who will stay on message and, objectively speaking, not hurt his own campaign -- then I have one word for you. Stop. Really. Because it just isn't going to happen.

The latest example of Trump's self-destructive tendencies came Friday morning, about 12 hours after a speech at the Republican National Convention that even Trump critics like CNN's S.E. Cupp praised for suggesting he might have "the discipline so many believed he lacks."

Here was Trump in front of his convention staffers and volunteers with the national media watching. This was truly an ideal opportunity to hammer home his campaign themes and attack Hillary Clinton after a convention that was, in truth, a bit of a mess. But instead, Trump used this press conference to settle a score with Ted Cruz, who had defiantly refused to endorse Trump a few days before.

And not only did Trump ridicule Cruz. In a jaw-dropping moment, he chose to resurface the allegation that Cruz's father was somehow linked to the assassination of John F. Kennedy, a claim that had been debunked as a "Pants on fire" lie by Politifact when Trump originally raised the issue in May. Trump went on to praise the National Enquirer as deserving of a "Pulitzer Prize" for some of its reporting.

Unsurprisingly, the headlines from his press conference were all about these comments, not Trump's campaign themes.

Yes, we all know Trump's supporters love it when he does this type of stuff. But here's the thing: the GOP primaries are over. We are in the general election phase, and Trump will need to expand his base or he very easily could lose. No doubt Trump knows this, too.

So the obvious question is why won't Trump stay on message and stop effectively sabotaging his own campaign? Simple: He can't help himself for two reasons.

First, Trump thrives on entertaining his fans, even if it's detrimental in terms of the big picture. He even admitted as much in April on Fox News when he candidly stated , "I can tell you that if I go too presidential, people are going to be very bored," adding some in the audience might "fall asleep." And just a few weeks ago Trump remarked at a packed campaign rally that if he stuck to using a Teleprompter, "I'd have about 12 people here instead of 7,000."

Trump sounds less like a presidential candidate focused on substantive issues and more like a performer whose priority is to pack the house and entertain the audience.

Indeed, at Friday's press conference, Trump "performed" for his supporters once again, including an impression of Ted Cruz. Entertaining, yes. But way off message. He did the same thing a few weeks ago at a rally, going so far off message that The New York Times dubbed it "a striking display of self-sabotage."

While I have never met Trump, I have known many "Trump" type comedians in the years I've performed stand-up comedy. They, like Trump, are often self-sabotaging in terms of their careers. For example, some are so seduced by the big laughs they will perform material that they know won't help in the long run, but which can be very crowd-pleasing in the short-term. (This can range from sexually graphic material to jokes extremely derivative of those used by better-known comedians.)

Some of these comics have tried to "pivot" to more original comedy. The problem is that their new material typically isn't as crowd-pleasing. So they soon revert back to the old material, even though they know it will likely ultimately hurt their career. Trump is cut from the same cloth.

Another similarity I've noticed between Trump and some of the comedians I know is that he appears to be narcissistic in the extreme. That's just not my opinion, but one also seemingly shared by various health care professionals

This personality trait can lead to arrogance and insecurity, and can drive people to lash out at critics. In fact, Trump has done just that for years -- responding harshly to anyone critical of him, from fellow politicians like Cruz to the media to comedians like Jon Stewart, who Trump tweeted about in 2013 after Stewart ridiculed his intelligence: "I promise you that I'm much smarter than Jonathan Leibowitz -- I mean Jon Stewart @TheDailyShow. Who, by the way, is totally overrated."

The bottom line? We can forget about Trump ever being presidential. Trump's desperate need to entertain, and his consistently demonstrated narcissism, may make for an interesting combination of personality traits when we're talking about comedians.

But he isn't auditioning for a chance to share his latest stand-up routine on stage. He is running to become president of the United States. And that truly would be a disaster.