The last time America disengaged from the world remotely in this manner was in the 1930s, and you remember what followed: World War II.

You have no idea how quickly institutions like NATO and the E.U. and the World Trade Organization and just basic global norms — like thou shalt not kill and dismember a journalist in your own consulate — can unravel when America goes AWOL or haywire under a shameless isolated president.

But this is not just about the world, it’s about the minimum decorum and stability we expect from our president. If the C.E.O. of any public company in America behaved like Trump has over the past two years — constantly lying, tossing out aides like they were Kleenex, tweeting endlessly like a teenager, ignoring the advice of experts — he or she would have been fired by the board of directors long ago. Should we expect less for our president?

That’s what the financial markets are now asking. For the first two years of the Trump presidency the markets treated his dishonesty and craziness as background noise to all the soaring corporate profits and stocks. But that is no longer the case. Trump has markets worried.

The instability Trump is generating — including his attacks on the chairman of the Federal Reserve — is causing investors to wonder where the economic and geopolitical management will come from as the economy slows down. What if we’re plunged into an economic crisis and we have a president whose first instinct is always to blame others and who’s already purged from his side the most sober adults willing to tell him that his vaunted “gut instincts” have no grounding in economics or in law or in common sense. Mattis was the last one.

We are now left with the B team — all the people who were ready to take the jobs that Trump’s first team either resigned from — because they could not countenance his lying, chaos and ignorance — or were fired from for the same reasons.

I seriously doubt that any of these B- players would have been hired by any other administration. Not only do they not inspire confidence in a crisis, but they are all walking around knowing that Trump would stab every one of them in the back with his Twitter knife, at any moment, if it served him. This makes them even less effective.