@DaveO276 I think the stated view is that the President has been authorized by Congress in past legislation to authorized or ban the travel of all aliens or certain classes of aliens and that, since Congress gave this power, congress can remove it. this view is reflected here, for example:

[heritage.org]

That view may well be the right view. But I suspect that a case could be made that, as the Commander-in-Chief whose duty it is to protect the country from its enemies, the President must be able to restrict the entry of certain aliens or classes of aliens in order to perform that duty. In fact, I suspect an argument could be made that the Congress tacitly recognized that this must be the case when it passed the previous law. But, then, a previous President also signed that into law and, it could be argued, tacitly agreed that Congress itself actually gave him the authority via its own Constitutional powers. Now, I'm no Constitutional scholar either, but I would sure like to see such a debate.