DACA has never been declared unconstituional or legal in a court of law and it has  gone to the Supreme Court (you may recall the court was split and Gorsuch had yet to be confirmed). So the SCOTUS could not rule it unconstitutional. There is a letter from 100 constutional lawyers and law professors who state their conclusion that the law is legal and constitutional. The persons who have registered and qualified for DACA are here legally and they are documented under a legal program. Trump is now turning them into illegals.