This article (January 2019) is a Trump hit (fear-porn) piece, but it actually does a good job of spelling out the vast powers a POTUS has under a state of emergency. Interesting read.

The Alarming Scope of the President’s Emergency Powers

From seizing control of the internet to declaring martial law, President Trump may legally do all kinds of extraordinary things.

"The moment the president declares a “national emergency”—a decision that is entirely within his discretion—he is able to set aside many of the legal limits on his authority."

MOAR:

https://www.theatlantic.com/magazine/archive/2019/01/presidential-emergency-powers/576418/