If the United States does not lead in a crisis, it will ultimately lose. Perhaps not right away, but U.S. power, security and influence will suffer. Others will step in and will act in their interests, not ours.

The president’s leadership standing is weak at the moment at home and abroad. Recent polls indicate declining approval for him in the United States and worse overseas. Chancellor Angela Merkel of Germany has made clear that the Europeans can no longer rely on U.S. leadership and must consider acting without us.

Imagine a foreign-policy crisis in which the president must rally U.S. allies. Will they listen? If he has to provide U.S. intelligence to them, which is standard practice, will they believe it after he has repeatedly said he is not convinced that that Russians interfered in the 2016 elections? For that matter, will the American people believe him?