At first sight, Donald Trump’s presidency might seem to prove that, in the end, people can get used to anything. Mr Trump’s election two years ago was an enormous shock to the American system. Soon, however, many persuaded themselves that the system would find ways of working around the Trump threat. There was much talk of “adults in the room” in the administration who would protect American values, interests and alliances from the interloper. On Wall Street, financial markets took a similar bet. However reckless the president, they concluded, he would not be permitted to make policy that would affect share prices and corporate profits.

Two years on, it is clearer than before that this was a complacent view. In the Trump White House, the once vaunted grownups, some of them from the military, have all been shown the door – most recently the defence secretary, James Mattis, who quit this month over the president’s unilateral decision to withdraw US troops from Syria. Now, it has become clear that the markets also called it wrong about Mr Trump. For days the White House has attacked the Federal Reserve over interest rates, and then, when the markets plunged, has rushed to reassure them that the Fed chairman, Jerome Powell, is safe in his job. The mayhem went on on Thursday. There was a 1,000-point recovery on Wall Street on Wednesday after a 600-plus point fall in the Dow Jones index on Christmas Eve. But the index is still down more than 3,000 points this month amid the continuing confusion.

Those who always despised Mr Trump are entitled to point out that this is what they said all along. But this is not just another Trump shock moment. The significant thing happening in America right now is that the undecideds are beginning to come off the fence. Even some generally cautious observers of the American scene now seem to accept that the Trump problem keeps on growing and that the “work-around” options no longer have credibility. “Last week was a watershed moment for me,” says one of these observers, the New York Times columnist Thomas Friedman. He wrote on Monday, amid the attacks on Mr Powell: “People wanted disruption, but too often Trump has given us destruction, distraction, debasement and sheer ignorance.”

Two other events of this week need to be seen in this context. Mr Trump’s first, typically bumptious visit as president to Iraq (in which he refused to meet Iraqi leaders or leave the US airbase) was a classic debasement, topped off by the Trump trademark of an outright lie about a pay rise to the military and by the shameless claim that the US, which unilaterally invaded Iraq, are “no longer the suckers”. Meanwhile, the budget impasse with Congress that led to the federal government shutdown last week is a classic Trump distraction, in which the only consistent thing about the president’s random daily comments is that they are invariably untrue.

This is not just the disruptive Trump presidency that many voted for and some at first decided to put up with. It is a different phase in the Trump era, in which the stakes are higher. Mr Trump now faces both the climax of the Mueller investigation and, from next week, the Democrat takeover in the House of Representatives. Both have the potential to put the president under legal and political pressures that, until now, he has not had to cope with. Mr Trump’s increasingly erratic belligerency is not simply a display of his own continuing unsuitability for the presidency. It is the behaviour of a president who sees the threats facing him and whose instability is such that he may try to pull the temple down with him.