Trump has not yet made a decision to declare a national emergency and order the military to build his fantasy border wall, but the Trump regime has begun preparing for the possibility.
The White House has directed the Army Corps of Engineers to determine if they can divert money from real emergencies to pay for Trump's fake emergency.
From the Associated Press:
The White House has directed the Army Corps of Engineers to comb through its budget in search of money for the wall, including looking at $13.9 billion in unspent disaster relief funds earmarked for areas including hurricane-damaged Puerto Rico, Texas and more than a dozen other states. That’s according to a congressional aide and administration official familiar with the matter who spoke on condition of anonymity because they were not authorized to speak publicly about the request. [...]
On Friday, officials in Puerto Rico said diverting disaster money to the wall was “unacceptable” and that the island was struggling to recover from Hurricane Maria, the Category 4 storm that hit more than a year ago and caused more than $100 billion in damage
I'm skeptical that a federal court would tell the "president" he cannot declare a national emergency even if no emergency exists, but I do believe a federal court would stop him from diverting funds that Congress appropriated for other specific reasons.
This appears unconstitutional at face value, but to my knowledge nothing like this has been tested in court before.
Legality aside, that idea that money should be diverted from Puerto Rico or from burn sites in California to make a down payment on Trump's wall is obviously monstrous. Trump doesn't give two shits about the humans who live in these disaster areas. His number one priority is himself and his own aspirations.