The Trump presidency is testing the American Constitution. Mr. Trump is going about the business of being president in bizarre and troubling ways. He started by showing an intention to govern by presidential decree and issuing presidential orders right and left. That did not go well. Many of his orders were ill prepared, many have been of little consequence, some have been slapped down by the courts.

It should, however, have gone worse. He set out to govern without Congress as an equitable partner. Congress did react, for example by turning down his initial health care “reform.” But Congress as such has not stood up to a president who has tried to side-line and diminish it as an institution.

Then followed a parade of executive incompetence and irregularity – in appointments, in a failure to make appointments and fill essential posts, in stimulating internal demoralising and chaos in the White House and the broader executive branch, in the spreading of misleading and untruthful “information,” in the boastful leaking by the president himself of sensitive security information to a foreign adversary, in an attempt to make the FBI an instrument of the president personally, in the firing of the FBI director who refused to comply, in various presidential actions to interfere with and pervert the course of justice.

The constitutional system has not failed to react. Congressional committees are investigating possible wrongdoings by the president and his team. The Justice Department has appointed a special prosecutor to investigate the same wrongdoings within a framework of criminal justice.

There should, however, have been more reaction. There is a power struggle going on. That struggle is for an imperial (if incompetent) presidency and against Congress. It is a messy and ugly power struggle, but unless the president’s usurpation of power is resisted, facts will be established on the ground and Congress will be further diminished. Congress has for years allowed itself to slip towards irrelevance. It is now as if a president with lust for power is exploiting Congress’s confusion about itself to govern unconstitutionally.

The pride of the American Constitution is “checks and balances.” It is designed to check the president so that he/she cannot attain despotic power. The framers assumed that presidents may incline to despotism and that such risks need to be controlled. It is possible, perhaps probable, that the Constitution will stand this test up against the kind of president the framers feared. But it is not assured. Mr. Trump has already lashed out against the Constitution itself as “archaic” and “a bad thing for the country,” and blamed it for the chaotic state of this presidency. A possible scenario is that Congress asserts itself to check the president, that the president takes this as an attack on himself and his mandate and fights back, and that the country is plunged into deeper constitutional crisis.

It is the responsibility of Congress to check the president. Congress may still do that. But so far, Congress has not risen above party politics to assert itself as an institution. Members of Congress, on both sides of the aisle, are still allowing the president to hold the initiative and mainly responding strategically by what is expedient for their own standing and electoral prospects. That’s what members of Congress must do, but it is not all they should do.

When a president persists in ruling against rather than with Congress, a time comes when Congress must stand up and act as an institution with independent judgement that goes beyond political expediency. Whether Congress would so do, is for now an open question. It is today a weakened institution which may not be able to harness the necessary collective will. An unpalatable president may win the power struggle and prevail over a further diminished Congress.