Update: shortly after 6pm, Steven Mnuchin posted a pair of tweets in which he denied that Trump had ever suggested firing Powell, which of course is to be expected: after all it was Mnuchin who picked Powell and it was Mnuchin who was blamed on several occasions by the president for picking the former lawyer as Fed chair:

(1/2) I have spoken with the President @realDonaldTrump and he said “I totally disagree with Fed policy. I think the increasing of interest rates and the shrinking of the Fed portfolio is an absolute terrible thing to do at this time,... — Steven Mnuchin (@stevenmnuchin1) December 22, 2018

(2/2) especially in light of my major trade negotiations which are ongoing, but I never suggested firing Chairman Jay Powell, nor do I believe I have the right to do so.” — Steven Mnuchin (@stevenmnuchin1) December 22, 2018

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if amid the barrage of negative news hitting the market this quarter there has been one outstanding item which would have sent it sharply (even) lower, that would be a flashing red headline - or a tweet from the president - announcing that Trump has fired Fed Chair Jerome Powell.

And while to many such an act would seem unthinkable, even from someone as unorthodox and unpredictable as Trump, it now appears that's precisely the outcome the market will have to worry about next as Bloomberg reports that the president has discussed firing Federal Reserve Chairman Jerome Powell "as his frustration with the central bank chief intensified following this week’s interest-rate increase and months of stock-market losses", citing four people familiar with the matter.

While advisors in Trump's inner circle have rightfully warned him that firing Powell would be a "disastrous move" for stock prices, and instead are "hoping that the president’s latest bout of anger will dissipate over the holidays", the sources reveal that the president - who is facing the imminent departure of two of his closest advisors, chief of staff Kelly and secretary of defense Mattis - has talked privately about firing Powell many times in the past few days.

Still, even Trump likely realizes that any attempt to push out Powell would have a devastating effect on the one barometer of his presidency he holds dearest to his heart - the stock market - and not only that, but terminating the Fed chair would likely send a shockwave across global financial markets, resulting in a collapse of risk asset prices and undermining investor confidence in the central bank’s ability to guide the economy without political interference. Worse, it would come at the worst possible time, just as markets are in freefall in recent weeks, with the Nasdaq just entering a bear market and the S&P less than 3% away from being 20% down from its all time highs.

It is likely that any move against Powell would be met by considerable legalistic resistance as it is unclear how much legal authority the president has to fire Powell, as the Federal Reserve Act says governors may be "removed for cause by the President" and since the chairman is also a governor, that umbrella definition also extends to him. Even so, the rules around firing the leader are legally ambiguous according to Peter Conti-Brown of the University of Pennsylvania notes in his book on Fed independence.

Additionally, while the Fed is independent only on paper, and history is replete with examples of presidents influencing monetary policy in the past, most notably when LBJ literally attacked then Fed chairman William McChesney Martin, there has yet to be an instance of an acting Fed chair being fired by the president.

Such a move would represent an unprecedented challenge to the Fed’s independence. Though he was nominated by the president, Powell was thought to be insulated from Trump’s dissatisfaction by a tradition of respect for the independence of the central bank. That separation of politics from monetary policy is supposed to instill confidence that Fed officials will do what’s right for the economy over the long term rather than bend to the short-term whims of a politician.

The reason behind Trump's ire is simple: he sees the Fed's rate hikes as the cause behind the market's recent slump, and after explicitly "urging" the Fed not to hike rates last week, saying Powell was "being too aggressive, far too aggressive, actually far too aggressive" and telling Reuters the central bank “would be foolish” to proceed with a rate hike, he may well see Powell's "not so dovish" rate hike as an open act of defiance - usually a career-ending move for anyone who ultimately is accountable to Trump.

The irony is that just over two years ago, Trump attacked Powell's predecessor, Janet Yellen, for creating a stock market bubble with her dovish policies: in Sept 2016, Trump accused the the Fed of "keeping the rates artificially low so the economy doesn't go down so that Obama can say that he did a good job. They're keeping the rates artificially low so that Obama can go out and play golf in January and say that he did a good job. It's a very false economy. We have a bad economy, everybody understands that but it's a false economy."

Two years later, when the same "false economy" belongs to Trump, the president has changed his tune, and his ideal Fed chair would be none other than Janet Yellen (whom Trump refused to reappoint for being "too short.")

The even bigger irony is that Powell finds himself in a lose-lose situation: one one hand he can merely perpetuate the unsustainable asset bubble created by his predecessors Greenspan, Bernanke and Yellen whose inevitable bursting would have devastating consequences on the financial system (which, however, he can leave to his successor as both Bernanke and Yellen did), or he can bit the bullet and be the one responsible for at least attempting the renormalization of monetary policies, an even which inevitably lead to far greater pain for those who invested in said bubble.

Furthermore, when Trump signed up for the presidency he should have picked one of the two options: the fact that he did not and two years later decided to continue on the autopilot set previously by the Fed is precisely why it is Trump who will now have no choice but to be the fall guy for the mess prior administrations, and previous Fed chairs created.

Trump’s public and private complaints about members of his administration have often been a first step toward their departures -- including former Attorney General Jeff Sessions, his first Secretary of State Rex Tillerson and outgoing chief of staff John Kelly.

And while it's not just Powell who is on the chopping block as some of Trump’s recent anger has also been directed at Treasury Secretary Steven Mnuchin for his part in persuading the president to select Powell to lead the Fed, the fact that Powell's tenure is now in jeopardy and that the Fed Chair could be fired after even a mere sharp drop in the market - with an S&P500 bear market looming as a likely psychological catalyst - will lead to a self-fulfilling prophecy as traders will now sell merely on the fear of, and frontrunning the news that Trump has fired Powell precisely as a result of such selling.