As President Trump stumbled from crisis to crisis this past week, he reminded the country of a lesson it didn’t really need to learn: A president’s greatest asset is trust. Once he has lost it, he can’t govern. Mr. Trump’s serial recklessness may change not just the course of his presidency but also the office itself. Whatever happens to him, it’s not too soon to wonder what will happen to the presidency when he’s gone.

For decades, the power of the executive branch has been growing, a trend that Congress has encouraged, both actively and by default. And the courts, the other check on the executive, have often been willing to defer to the president’s prerogatives.

But President Trump’s words and actions are straining the relationship between the executive and the other branches of government in ways that may ultimately diminish the power of the office. By showing he’s unworthy of the trust that a president customarily enjoys, Mr. Trump has essentially been daring Congress, the courts and even the bureaucracy to act against him.

And those institutions are taking him on.

The firing of James Comey as F.B.I. director illustrates how the president’s rash words have invited the trouble he now finds himself in, paving the way to last week’s appointment of a special counsel by the Justice Department to investigate potential ties between Mr. Trump’s campaign and Russian meddling in the election.