This means he will likely sue and seek a Federal Court order.
When the municipality violates it, every paid official is subject to contempt, or worse, charges. The judge can order them to jail in 24hrs.
Which is what will happen if they go on TV saying they will not comply with the court order.
And, the POTUS can Federalize the National Guard of any state to remove obstructions to the implementation of Federal Law.
It would be sweet indeed to have the same power which enforced Brown vs Board of Education in Alabama now be used to enforce immigration law.
Yes, nothing could be sweeter than to see the federal government actually enforcing immigration law by arresting those enabling it and deporting the law breaking illegals.