Especially when it comes to national security, there is a premium on an administration speaking clearly, consistently and precisely, starting with the president.
It is not O.K. for one sovereignty to dictate to another which countries or organizations it may associate with.
It's one thing for a foreign partner to doubt a president's judgment; it's entirely more debilitating when that partner doubts the president's word.
Every country has a founding mythology. For Americans, it starts with our first president's youthful encounter with a cherry tree and refusal to tell a lie. Mr. Trump would do well to find inspiration in that story, which goes to the heart of what makes America different - and our foreign policy effective - around the world.
Mr. Trump knows that banning travel to the United States from a half dozen Muslim-majority countries would do nothing to enhance our security - and everything to undermine it.
By alienating Muslim communities and our closest allies, Mr. Trump would destroy the partnerships we need to effectively fight terror.
Mr. Trump's travel ban has never really been about security. Rather, it's the tip of the spear in a much broader battle: to drastically curtail immigration to the United States that is changing the complexion of our country.