I think it's highly unlikely he'll declare a national emergency. I imagine he's getting tons of push back on the idea from Republicans who realize there would be nothing to stop a future Dem POTUS from doing the same in the name of gun violence or climate change. Terrible idea and I doubt courts would allow him to get away with it. Democrats will give him money for border security but not for a wall and that's what will pass sometime in the next 3 weeks.