Whenever the President finds that the entry of any aliens or of any class of aliens into the United States would be detrimental to the interests of the United States, he may by proclamation, and for such period as he shall deem necessary, suspend the entry of all aliens or any class of aliens as immigrants or nonimmigrants, or impose on the entry of aliens any restrictions he may deem to be appropriate. Whenever the Attorney General finds that a commercial airline has failed to comply with regulations of the Attorney General relating to requirements of airlines for the detection of fraudulent documents used by passengers traveling to the United States (including the training of personnel in such detection), the Attorney General may suspend the entry of some or all aliens transported to the United States by such airline.

The discretion here is extremely broad — and is presumably supplemented by the President’s executive power in relation to foreign affairs and national security. The core of President Trump’s executive order may well be a lawful exercise of his broad discretion. Yet the manner of its exercise and the ensuing chaos over the weekend point to the practical constraints under which President Trump operates.

It is useful to begin with the observation attributed to Einstein: everything should be made as simple as possible, but no simpler. President Trump’s executive order sweeps extremely broadly. It identifies seven countries (which were already subject to restrictions) from which immigrants to the United States are no longer welcome.

But problems of interpretation abound. Does it apply to green card holders, who are permanent residents of the United States by virtue of a process conducted under statutory authority? Does it apply to others who have been granted visas (to study, to work and so on), again under statutory authority? When the order refers to “entry”, what does it mean — an individual’s first entry only or any subsequent re-entry? Does it apply to dual nationals, who may be a national of one of the seven countries and a national of another country, including American allies such as Canada and the United Kingdom? Does it apply to nationals of the seven countries who are travelling to the United States from a different country, where, indeed, they might be permanent residents?

Whatever one’s views of the merits of President Trump’s immigration policy, these problems of interpretation have caused significant confusion and, indeed, hardship. Ordinarily, an order like this one would go through a process of consultation with the agencies charged with administering it. The interpretive questions I listed above would have been resolved before the policy was put into action. Border agents would have been advised, perhaps even trained, on how to administer the policy.

There is an important general (though not original) point here about the constraints of law. When you seek to regulate by law, you become subject to certain constraints, chief among them the need to rely on others to implement and interpret your commands. When you cut the implementers and interpreters out of the decision-making loop, your ability to achieve your regulatory goals is compromised. President Trump could probably achieve his goals without going through a process of consultation, but it would be extremely difficult for him to do so.

Nonetheless, it would be naive to ignore some of the other constraints President Trump is operating under. Many members of the federal bureaucracy do not agree with his policy goals. They have leaked details of proposed policies. Some law professors have advocated civil disobedience by bureaucrats. All of this is understandable but it may be counter-productive. Had President Trump embarked upon the usual course of interagency policy consultation before drafting his executive order it is highly likely that the details would have leaked, provoking a significant domestic and international backlash. President Trump must contend with the backlash now but, symbolically, he has demonstrated that he is ‘in control’: the rest of us are dancing to his tune, not the other way around.