The Brains Trust - 2020, page-5

I don't know much about military law and whatnot, but I am pretty sure at the least targetting non-military sites where there are known to be civilians would at least breach parts of the Geneva Convention. Lets hope that is nothing but bluster, as is often the case with Trump.

"Articles 51 and 54 outlaw indiscriminate attacks on civilian populations, and destruction of food, water, and other materials needed for survival. Indiscriminate attacks include directly attacking civilian (non-military) targets, but also using technology such as biological weapons, nuclear weapons and land mines, whose scope of destruction cannot be limited. A total war that does not distinguish between civilian and military targets is considered a war crime."
Source:
https://en.wikipedia.org/wiki/Protocol_I