Editor's Note: This article is one of 50 in a series about Trump's first two years as president.

Unlike pornography, a constitutional crisis is not always obvious when you see it. The question of whether the nation is in the grip of such a crisis first surfaced within weeks of President Donald Trump’s inauguration, and it has never really gone away.

After the first travel ban was issued, in January 2017, stories emerged of Customs and Border Protection agents disobeying court orders to halt implementation of Trump’s executive order. Although the disobedience in question turned out to be more the product of confusion than systematic overthrow of the rule of law, the term constitutional crisis was thrown around quite a bit. Those two little words again took over headlines after Trump fired FBI Director James Comey in May 2017, and when he seemed poised to dismiss Special Counsel Robert Mueller or even pardon himself. Former Secretary of State John Kerry suggested that a crisis had arrived in response to the anonymous New York Times op-ed by an administration official supposedly working to stymie the president’s wilder impulses. A recent Supreme Court filing challenging Matthew Whitaker’s replacement of Jeff Sessions at the Justice Department referred to Whitaker’s appointment as a “constitutional crisis.”

There is no standard definition of what makes a constitutional crisis as a matter of law or history. Under the Trump administration, suggesting the arrival of such a crisis evokes a mood more than anything else—a sense of ineffable, fractured dread.

Keith Whittington writes that constitutional crises entail “circumstances in which the constitutional order itself is failing”; Sanford Levinson and Jack M. Balkin similarly define such a crisis as “a potentially decisive turning point in the direction of the constitutional order, a moment at which the order threatens to break down.” Most people seem to agree that if Trump were to fire the special counsel in an effort to shut down the investigation into his conduct, the term constitutional crisis could fairly be applied. Despite the dire predictions, however, that may never come to pass. As Jack Goldsmith has argued, the Justice Department has proved resilient to the president’s most egregious assaults. The president has not succeeded in removing Mueller; the Russia investigation appears to have continued on course even under Whitaker’s uncertain supervision. Meanwhile, an independent investigation into campaign-finance violations committed by Trump’s former lawyer Michael Cohen appears to be circling closer and closer to the president.

And yet, a sense of dread remains. To be overly sanguine about the health of the republic because the one obviously crisis-triggering event has not occurred risks following the circular logic of Republicans who have refused to act to protect the Mueller investigation because the president has not yet shut it down. “If there were an occasion, I would be rising to it,” the humor columnist Alexandra Petri wrote in a devastating description of this reasoning.

It may be wiser to focus less on crisis than on constitutional rot, what the constitutional scholar John Finn describes as the slow erosion of faith in the underlying ideals of the republic, even as legal structures seem to remain in place. Rot is not grand. It is the patient assault of base creatures like fungus and bacteria. But at some point, the floorboards fall apart.

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