This article explains why it is highly unlikely there's anything Trump can do to ban bump stocks. It is also highly unlikely that he doesn't already know this, and it's only a PR move on his part where it will be kicked to the Republican Congress, where all good things go to die. Via a piece from CBS News that appeared after the Las Vegas shooting:

The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) is the federal agency that reviewed the bump stock device manufactured by the company Slide Fire and determined in 2010 that the accessory complied with the law. Machines guns have been outlawed since 1986. ATF officials determined in their evaluation of the product that it could not be regulated by the agency.

"The stock has no automatically functioning mechanical parts or springs and performs no automatic mechanical function when installed," John Spencer, the chief of the ATF's Firearms Technology Branch, wrote to Slide Fire in a 2010 letter. "We find that the "bump-stock" is a firearm part and is not regulated as a firearm under Gun Control Act [GCA] or the National Firearms Act [NFA]."

But banning bump stocks won't solve the problem when it's so simple to convert these guns to fully automatic. Here's a shooter with his assault weapon- and a rubber band:

So at least some assault weapons can be easily converted into fully automatic with a rubber band. And as the top video demonstrates, with some guns, you don't even need a rubber band! Obviously, there are easy ways to get around the automatic firing restrictions.

Food for thought -- and for members of the media.