If the president tries an autocratic end-run around the Constitution and declares an national emergency to build his wall, the legal problems he has with the Southern District of New York, the New York State Attorney General's office and the Mueller investigation will pale in the face of the lawsuits he will face when he tries to use Eminent Domain to steal property along the border.
Additionally, he will have to win every environmental impact suit and God knows what else the legal system will throw at him before the first shovel of dirt is turned over. The suits to stop a simple power line across the James River took almost a decade; hundreds of miles of wall will take 100 times longer. The president will be long dead and buried before his first fence post is set.
His childish behavior is, in part, the product of his belief that the law does not apply to him. He behaves like someone who has never had anyone say no to what he wants, and as part of his vision as president, he feels he can act as though he were a Roman Emperor, whose every whim is law.
He appears to have no understanding of the presidency and the legal and Constitutional restraints on his actions.
Sadly, we the American people will have live with the results of this behavior well into the future. His childish behavior is not limited to this pipe-dream of a wall, but is seen in everything he does on the world stage and the damage is piling up like wind-driven snow against a hedgerow.