Incredibly the military has already fought AGAINST being used to patrol the borders.
According to CNN's anonymous sources, the "Pentagon rejected request for troops it viewed as emergency law enforcement at border"
https://www.cnn.com/2018/11/02/politics/white-house-pentagon-troops-border/index.html.
CNN helpfully emphasized the key legal issue: "Despite multiple defense officials characterizing those activities as relating to law enforcement actions, a DHS official disagreed that such functions constituted law enforcement."
Intimidation is a problem, because the law imposes prison or a $10,000 fine on any military official violating it. So the military does not want to perform these tasks unless the law is crystal clear. DoD has invented a lot of its own rules more restrictive than the Act itself.
The Pentagon does not refuse requests. It takes orders. Period. The president does not ask the Pentagon for permission to use troops. He orders.
Fake news from anons... is still fake.