Answer: Executive Order
Step-by-step explanation:
One of the powers that the President has is to be able to issue Executive orders. The President is the head of the Executive and as such can issue an Executive order which is a directive to the departments and agencies under them to do something.
An Executive Order carries the full weight of law and can only be counteracted by the Judiciary declaring it Unconstitutional or Congress passing a law against it but that law would have to be signed by the President so that path is challenging.