Dean Obeidallah, a former attorney, is the host of SiriusXM radio's daily program "The Dean Obeidallah Show" and a columnist for The Daily Beast. Follow him @DeanObeidallah . The opinions expressed in this commentary are his own.

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In its cold open, "Saturday Night Live" featured two A-list cameos: Ben Stiller and Robert De Niro. While both did an excellent job, one was absolutely perfect.

First, there was Ben Stiller doing an uncanny impression of Donald Trump's personal lawyer Michael Cohen, or as Stiller described him: "Michael Cohen, attorney at law. And also sometimes not at law." Stiller delivered some of the funniest lines of this sketch, including this one in reference to the recent FBI raid of Cohen's office and hotel room: "Can you believe what they're doing to poor Mr. Trump? It's a disgrace! This whole raid was a complete violation of attorney-criminal privilege."

But the perfection was De Niro as Robert Mueller -- and not just from a comedic point of view, though it gave De Niro and Stiller the opportunity to recreate a famous scene from their hit movie, "Meet the Parents." The perfection comes from the fact it appears that Trump is truly afraid of both De Niro and Mueller.

Clearly, Trump is fearful of Mueller's investigation -- and he appears to have every reason to be. By all accounts, Mueller is a laser-focused public servant who is getting results, as proven by the guilty pleas of people like Trump's former national security adviser Michael Flynn and the complex money laundering case he is bringing against Trump's one-time campaign manager, Paul Manafort. Consequently, it comes as no surprise that Trump reportedly was on the verge of firing Mueller on two occasions to stop his investigation. But the fact Trump hasn't canned Mueller yet despite White House press secretary Sarah Huckabee Sanders recently making it clear Trump "certainly believes he has the power" to do just that, adds to the sense Trump fears Mueller.

That's why having De Niro play Mueller is spot on. Trump, it would appear, also has some trepidations about De Niro. We all know Trump famously lashes out against people who publicly slam him. As Melania Trump said , the Trump doctrine is essentially if "you attack him, he will punch back 10 times harder."

Yet for some reason, despite De Niro's relentless attacks against Trump, we haven't seen Trump punch back at De Niro. And I'm not talking subtle little jabs by De Niro. It's more akin to the scene from "Goodfellas" where De Niro has been pummeling Trump like a guy who failed to pay out on a bet he lost.

In fact, during the campaign, in a video that went viral, De Niro said he'd like to physically attack him: Trump "talks [about] how he wants to punch people in the face? Well, I'd like to punch him in the face." (De Niro was reacting to Trump's statement at his campaign rally about a protester: "I'd like to punch him in the face.")

In that video, De Niro also called Trump "a con, a bulls—t artist" and a "punk." But not a peep from Trump in response.

De Niro has continued with his personal and public slams of Trump right through today. For example, in an April 2017 television interview, De Niro said , "This guy has sullied the presidency. He's debased the presidency." In August 2017, De Niro made headlines when he called Trump "a flat-out blatant racist" adding, "if he [Trump] was smart, he'd be even more dangerous."

And De Niro stepped up his attacks in the last few months. In January 2018, the Academy Award winning actor, while speaking at the National Board of Review awards, served up a profanity laced takedown of Trump, dubbing him the "jerk-off in chief," and adding, "This f‑‑‑ing idiot is the President. It's 'The Emperor's New Clothes.' The guy is a f‑‑‑ing fool."

Just last month, De Niro did it again while speaking at an event for the Fulfillment Fund, a Los Angeles-based organization that promotes higher education. There, the 74-year-old actor explained that while he didn't want to turn the event into a political one, he felt compelled to speak out about Trump because, "to be silent in the face of such villainy is to be complicit." Adding, "It's especially appropriate tonight because Trump treats education as a con, a way to make a profit at the expense of the suckers."

Trump has not sent out even one tweet fighting back. This is even more curious given that, as The New York Times has documented, Trump has lashed out on Twitter at nearly 450 "people, places and things" since his 2016 campaign through today.

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And Trump has shown no hesitation to go after actors who have criticized him, from Alec Baldwin to Meryl Streep , who didn't even criticize Trump by name at an awards show in January 2017 but still Trump knew she was talking about him.

Why is Trump seemingly so afraid of De Niro? Could it be because they are both about the same age and from New York, so perhaps Trump fears if he goes after De Niro, he can expect a no holds barred street brawl?

It's unclear, but what is certain is that Trump fears both Mueller and De Niro, making them a modern-day version of "The Untouchables." At least until Trump works up the nerve to respond to De Niro or cause a constitutional crisis by firing Mueller. However, given Trump's legendary impulsiveness and the fact he has done neither yet is more proof that Trump the bully is truly scared of these two.