In one of the excerpts to this story, The Hill writes:
Trump also threatened to use emergency powers to build the wall, a move that would inflame tensions with Congress, where Democrats have taken control of the House, and raise legal questions about his executive authority.
In truth, Trump does have a defensible “Separation of Powers” claim here, and he has the option to ignore any of the Federal courts that might back his opponents challenging his “emergency powers.”
It’s important to remember that the judiciary has no authority, or leverage, to deny another branch from checking an offending branch’s attempt to usurp its own Separated Powers.
This is especially the case when one of the two parties in dispute is the Judiciary itself. After all, the most universal bedrock principle in law is that “no-one should be a judge in his own case.”
Thankfully, the highest ruling for such a conflict is with the Senate Trial – assuming the House impeaches Trump in objection to his Executive Branch Separation of Powers claim.
As long as Trump successfully enough makes his Separation of Powers claim to the point where the Senate doesn’t have the two thirds vote necessary to oust him, his actions would stand.
Since he will have one constitutionally, he will have one legally.
So, while the Judiciary has the final say on court rulings, it PROVABLY does not have the final say on governmental branch disputes.
And this makes sense because the only reason why Checks and Balances exist is because each branch of government has certain absolute powers beyond the reach of the other two, and each possesses a different way to implement said check.