https://www.nytimes.com/2019/01/07/us/politics/trump-national-emergency.html

«The recent caravans from Central America primarily consist of migrants who are not trying to sneak across the border but instead are presenting themselves to border officials and requesting asylum.

And while Mr. Trump and his aides keep claiming that terrorists are sneaking in across the border, including assertions that they are doing so by the thousands, as a matter of empirical reality, there has been no such instance in the modern era.

….

Why did Congress give presidents such broad power?

In part by accident.»