This is where the hardcore GOP and their supports need to be very careful. If by some craziness beyond all reason a supreme court side with the President(once more unlikely given everything) then you've just set precedence.
How can that same supreme court then say fools running up with Guns in the schools, towers in Vagas, Banks, groceries committing heinous crimes ISN'T an emergency? Unlike this so-called border emergency, there's a lot more documentation and numbers across the board to support it.
So, they may have finally provided the means for a President to legally deal with the gun emergency in this country.