MbS's problem is his family, who know perfectly well that he ordered the murder of Saudi journalist Jamal Khashoggi in the Saudi consulate in Istanbul, and understand what that crime means for the kingdom's standing in the world.
They also realise that his foreign policy has been an unmitigated disaster — from the futile war in Yemen to the blockade of Qatar — and that his economic policy hasn't been much better.
Many prominent Saudis also have personal reasons to hate him.
Some were pushed roughly aside in order to facilitate his rapid rise to supreme power. Others were kidnapped, jailed and even tortured in order to extort billions of dollars from them, on the often shaky pretext that their money was the fruit of corruption.
If you held a secret ballot among the 10,000 most influential Saudis, MbS would be gone in a flash.
It doesn't work like that, of course.
This is still an absolute monarchy, and so long as MbS has the support of his elderly father, King Salman, he has absolute power – in theory. In practice, he must also have at least the grudging support of the royal family, which sees the Saudi state as a family business in which they all have a stake.
It is a remarkable family, if only for its sheer size — an estimated 15,000 members, many of whom are direct descendants of the kingdom's founder, King Abdul-Aziz Ibn Saud.
When he died in 1953 he left 36 sons, and there are literally hundreds of grandsons.
All these men, their spouses and their children and grandchildren are supported (quite lavishly) by the family business, but there are only a few hundred people who really matter.
They matter a great deal, however, and by now they would be close to unanimous in seeing Muhammad bin Salman as a wrecker who is endangering their own futures.
So how to get rid of him? In the past, the family's rule has survived the abrupt removal of kings: one king was forced to abdicate in 1964, another was assassinated by his own nephew in 1975. The princes closed ranks, and the dynasty carried on with a new king.
In theory, it should be even easier when you are only trying to remove the crown prince.
Why not just work through his father, King Salman? After all, the king has already appointed and then dismissed two other crown princes; maybe he could be persuaded to do it again.
The problem with this approach is that MbS zealously controls access to the 82-year-old king, who is believed to be suffering from mild dementia (Alzheimer's).
An alternative would be for the Allegiance Committee, a family-run institution created in 2006 which adjudicates on succession issues, to declare King Salman incompetent because of illness, dismiss the Crown Prince, and appoint someone else as his successor.
In the absence of more formal rules, any prince descended from Abdul-Aziz would be eligible.
Plotters hoping to use this device would be risking their lives, of course, for MbS is a ruthless man who would strike first if he got wind of the plan.
However, they may be emboldened by the fact that he has now arrested his own chief enforcers in an attempt to shift the blame for Khashoggi's murder. This betrayal will certainly have shaken the loyalty of their colleagues who still serve the crown prince.
But there is one further consideration that is bound to give even the boldest plotters pause. If MbS concludes that he has decisively lost the support of the royal family, he still has a last card to play — war with Iran.
It's what he wants in the long term anyway, but his preferred option has been to get the United States and Israel to do the actual fighting for him.
If he had no other way of heading off a family-backed coup against him, however, he might take Saudi Arabia into such a war unilaterally, counting on the US and/or Israel to bail the country out. In the midst of a war, nobody at home would dare attack him.
So, on balance, MbS is likely to stay in power ... perhaps to the ultimate ruin of the country he rules.
Gwynne Dyer's new book is 'Growing Pains: The Future of Democracy (and Work)'
