(CNN) As a candidate, Donald Trump would famously boast that if elected, he'd "surround myself only with the best and most serious people" -- adding: "We want top-of-the-line professionals."

The first 18 months of his presidency have repeatedly revealed the fallacy of that pledge, as myriad members of Trump's Cabinet and senior staff have departed -- often under suspicious circumstances -- even as the President himself has railed against the ineptitude of people who still work for him.

Just this weekend, Trump dealt with two major staff problems -- both of which, in different ways -- he created.

The first was a series of interviews by Omarosa Manigault Newman, a former aide to the President, in which she alleged -- among other things -- that she had been offered money to stay silent after leaving the White House. Manigault Newman also claimed that she secretly taped White House chief of staff John Kelly firing her in the Situation Room. And on Monday morning, she released an audio recording to NBC's "Today" of an apparent phone conversation with Trump that suggested he was unaware of her firing before it happened.

(Omarosa's tell-all memoir of her time in the White House comes out this week.)

The second came when Trump -- amid a now-regular Twitter tirade regarding the special counsel probe -- derided Attorney General Jeff Sessions as "scared stiff and Missing in Action." (And, yes, that capitalization is in the original tweet.)

The twin episodes highlight the "why" behind the massive staff volatility in Trump's White House: He relies almost totally on his gut in the hiring process, he plays aides against each other for sport, he runs incredibly hot and cold on staff, and he is more than willing to publicly embarrass or shame those who work for him.

The Trump of "The Apprentice" -- which, by the way, is where the billionaire's path first crossed with Omarosa -- is the Trump that now sits behind the Resolute Desk in the Oval Office.

The difference is that Trump was solely playing for ratings on "The Apprentice," whereas now he is trying desperately to effectively run a government. Turnover -- or the threat of firings -- was the name of the game in Trump's reality TV world. In the White House, all of the turmoil adds to the already palpable sense of chaos that surrounds 1600 Pennsylvania Avenue.

Already, 57% of Trump's "A Team" staffers have left the White House in just its first year and a half, according to statistics maintained by Brookings Institute's Kathryn Dunn Tenpas . That nearly equals the turnover among top staffers for the entire first terms of Barack Obama (71% turnover), George W. Bush (63%), Bill Clinton (74%) and George H.W. Bush (66%).

(Tenpas' data may actually undersell the changes in Trump's administration, given that she only counts one departure for each office. So, while Trump has had five communications directors since being elected President, they only count as one departure in Tenpas' calculations.)

Focusing just on Cabinet secretaries, the numbers are equally stunning for Trump. He's already seen seven Cabinet officials -- three in his first year, four in his second -- leave in his first 18 months in office. Obama had zero Cabinet departures in his first year and four in his second. George W. Bush lost only four Cabinet members in the entirety of his first four years.

And then there is Sessions. No Cabinet member -- past or present -- has been bullied by Trump more than the nation's top law enforcement professional. Trump has repeatedly said publicly that he wishes he would have picked someone other than Sessions to be his attorney general -- due in large part to the fact that Sessions recused himself from the Justice Department's investigation into Russian interference in the 2016 election. Sessions did so because he was a prominent surrogate for Trump during that campaign. The President has never forgiven him.

Trump has referred to the former Alabama senator in tweets as "beleaguered," very weak" and "disgraceful." He has teased Sessions by referring to him as "Mr. Magoo." And on and on.

What Trump has not done, inexplicably, is fire Sessions. And neither has Sessions quit. Instead the two men remain locked in a what, to all the world, looks like a game of chicken between two willful teenagers. Sessions continues showing up to the Justice Department day in and day out. Trump takes to Twitter to attack his AG almost as often. Neither man blinks.

The result, like so much of Trump's wildly unpredictable management style, is disorder, disarray and disorganization. Turnover and uncertainty rarely create a well-functioning work environment. And because of Trump's tendency to openly discuss and deride both those who have left his side and those who continue to work within his administration, he launches a series of storylines that not only highlight the pandemonium within his ranks but also crowd out other, more positive stories for his White House. (The latest tweet on Sessions and the ongoing Omarosa mishigas are prime example of this latter reality; both of those narratives will drive this week's news cycles.)

Trump, at least outwardly, seems entirely unbothered by the constant churn within his senior staff.

"The one that matters is me," he told Fox News' Laura Ingraham last November . "I'm the only one that matters. Because when it comes to it, that's what the policy is going to be."

What that view overlooks is that running the federal government is not the same thing as running a business. Trump the businessman made a career out of relying only on himself and a very tight knit group of family and hangers-on. While he has tried to do the same in Washington -- his daughter and son-in-law both work for him in the White House -- he has met with far less success.

Whether Trump is playing the long game -- and that his consolidation of power will, in the end, create major wins for the country -- remains a topic of some debate. What is beyond argument is this: The first 18 months of Trump's administration make clear that his plan to bring together "the best and most serious people" has failed miserably.