Maybe you haven't quite grokked the meaning in the text of the law.
According to the applicable statute, the President is solely vested with the authority to suspend immigration from anywhere, or everywhere, if and when he deems such immigration to be detrimental to the national interest.
That's not making law "like Obama did."
But once they step on US soil then the other laws kick in. They become US persons. So the challenge is keeping them out before they get here.