Legally, this is the same as banning Jerry Miculek
Notice though he has not banned bump stocks 1 year after the Las Vegas shooting. So he is not just acting unilaterally to ban them. What is he doing exactly to ban them?
Here is President Trump at a news briefing back in Oct. 2018. He thought it would be 2 or 3 weeks back then to finally enact the ban. Perhaps he is finding that banning them is not really possible? At least he is going through procedures, and not creating his own laws. Also, the NRA said they would not fight a ban.
So everyone needs to wait until it happens, and how it happens, if it happens. As it stands right now, bump stocks are still allowed to be bought & sold.