I don't believe that an executive order is the means of dealing with the situation. It does set a bad precedent, but its one that the progressives would have no problem pulling the trigger on and would gleefully do so. Trump's executive order will be challenged in the supreme court and I believe at the end of the day it would pass. With that said, SCOTUS would also have to rule on progressive executive orders dealing with gun control and climate change. Both issues can be defended against on a constitutional basis and with the current make up of the court, I would think the odds are in the conservative favor.