At minimum, the president should name an extraordinarily good pick to replace Mr. Comey as FBI director. And he should either confirm his hints of a taping system in the Oval Office or else admit he was trolling us.

Maybe the 70-year-old president is too old to change, and Americans must simply accept his chaotic, unpredictable, impulsive nature. But if Mr. Trump can’t recognize he’s the cause of the turmoil, he risks creating a hard cap on his approval ratings in the low 40s or high 30s. This will drain his power, make it difficult to achieve his agenda, and turn him into a lame duck well before normal. If Mr. Trump can’t change his ways, he will fail the people who entrusted him with their hopes.

This presidency has reached a critical moment. For months, true-blue Trump supporters grimaced at tweets and winced at needless controversies, but stood firm. Now many are questioning whether their man is up to the job. Mr. Trump will not restore their confidence with the behavior he’s shown so far.