He was the head -- and most prominent face -- of his Trump business empire. He was the head -- and most prominent face -- of his hit reality TV shows: "The Apprentice" and "The Celebrity Apprentice." In both of those roles, what he said went -- without debate.

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The whole aura of Trump is based on the idea that he does what he wants, when he wants. If he wants you fired, you get fired.

All of which brings me to the ongoing investigation by special counsel Robert Mueller into Russia interference in the 2016 presidential campaign and the possibility of collusion between the Russians and members of the Trump campaign. And Trump's clear frustration -- and nervousness(?) -- about it.

Asked about the investigation on Friday, Trump said from the Oval Office: "I'm not agitated. It's a hoax. The whole thing is a hoax. There was no collusion."

"The inner workings of the Mueller investigation are a total mess. They have found no collusion and have gone absolutely nuts. They are screaming and shouting at people, horribly threatening them to come up with the answers they want. They are a disgrace to our Nation and don't care how many lives the ruin. These are Angry People, including the highly conflicted Bob Mueller, who worked for Obama for 8 years. They won't even look at all of the bad acts and crimes on the other side. A TOTAL WITCH HUNT LIKE NO OTHER IN AMERICAN HISTORY!"

It's not clear how Trump obtained information about the "inner workings" of the Mueller investigation given that special counsel's office has been tight-lipped about its approach -- only occasionally revealing something when a plea agreement is reached or when someone like Paul Manafort faces trial based on what Mueller's team uncovered. Given Trump's track record with the truth -- and his fixation on the idea that Mueller is conducting a witch hunt (even though he's not) -- the possibility certainly exists that Trump made up his alleged insider information about the Mueller probe.

The broader context here speaks to Trump's ever-mounting frustration with his inability to control the Mueller probe. We know -- thanks to CNN reporting -- that Trump spent several hours this week huddled with his attorneys going over written answers to questions that the Mueller team had submitted to the White House regarding the 2016 campaign.

That Trump's tweet on Mueller came after that intense period of question-answering provides our clearest evidence yet that Trump's anger and impatience is bubbling over. But it's far from the only sign.

The biggest indicator of Trump desperately trying to seize control of the uncontrollable came last Wednesday when Trump finally fired his long-maligned Attorney General Jeff Sessions . Trump had never forgiven Sessions for recusing himself from the FBI investigation into Russian interference; in Trump's mind, that decision by Sessions led to the formation of the special counsel and all of the problems Mueller's investigation has caused within Trump's administration. The firing of Sessions, however, was not the big news -- that was Trump's decision to bypass Deputy Attorney General Rod Rosenstein, who was overseeing the Mueller investigation, and instead name Matthew Whitaker as acting attorney general.

Suddenly, a public critic of the Mueller probe almost since its inception was in charge of its operations. (That Whitaker, who has not been confirmed by the Senate, is now in charge of people like Rosenstein, who does have Senate confirmation, is a also a potential legal hurdle .) And not only that, but Whitaker was selected over Rosenstein, who had been publicly supportive of Mueller and the probe generally.

Trump himself has also grown more and more boastful about what he could do to Mueller and the probe -- if he so chose. "I could fire everybody right now, but I don't want to stop it because politically I don't like stopping it," Trump said last week in the wake of the 2018 midterm elections (more on that in a minute). "It's a disgrace. It should never have been started, because there is no crime."

That's not technically accurate. The only person who could fire Mueller is the attorney general. So Trump could tell Whitaker to fire Mueller and, in theory, Whitaker could do that. (Whitaker has given no public indication whether he would be willing to follow that order from Trump.) There are legal and political issues that would naturally flow from such a move -- among them the question of whether Mueller can be fired without obvious cause and how Republicans (and Democrats) in Congress would react to the special counsel's investigation being ended.

Trump knows all of this. Which is what leads to his frustration. He's boxed in. He can't do what he wants to do. (Remember that Trump already tried to remove Mueller but was thwarted when then-White House counsel Donald McGahn refused to carry out the order.) He has no operational control over this situation.

When asked Friday about his latest tweets about Mueller, Trump said tellingly: "I like to take everything personally, because you do better that way."

Trump, when cornered, is at his most dangerous -- to his political opponents and, candidly, to himself. He lashes out. He veers even further from established truth and facts.

In short: The longer the Mueller probe continues, the more likely Trump is to say or do something with potentially cataclysmic impact on his administration (and the investigation). All outward signs indicate he's getting closer and closer to that sort of point of no return.