On Sunday, President Trump opened his speech at the annual Governor’s Ball by talking about the February 14 school shooting in Parkland, Florida:

We’re gonna have a lot of meetings tomorrow. We’re gonna have some very important meetings. We’ll be talking about Parkland, and the horrible event that took place last week ... that will be one of the subjects, and I think we'll make that first on our list, because we have to end our country of what's happening with respect to that subject.

On Monday, Trump told a gathering of state governors: “By the way, bump stocks, we’re writing that out. I am writing that out. I don’t care if Congress does it or not, I’m writing it out myself, ok? You put it into the machine gun category, which is what it is — it becomes essentially a machine gun...”

According to Business Insider, a bump stock "harnesses the recoil energy produced when a shot is fired from a semi-automatic rifle,” causing the firearm to bounce “back and forth between the shooter's shoulder and trigger finger,” thus allowing a semi-automatic rifle to fire more rapidly.

In the wake of the Parkland shooting, the president has made several moves pertaining to gun control, with a specific focus on bump stocks. On February 20, Trump directed Attorney General Jeff Sessions to “propose regulations that ban all devices that turn legal weapons into machine guns.”

There is doubt as to whether Trump can unilaterally ban bump stocks. In 2013, Richard Marianos, then-assistant director for public and governmental affairs at the Bureau of Alcohol, Tobacco, Firearms, and Explosive (ATF), sent a letter to Rep. Ed Perlmutter (D-CO) regarding bump stocks. The letter stated that certain types of bump stocks, ones that didn’t contain mechanisms to “automatically reset and activate the fire-control components of a firearm following the single input of a user,” were unable to be regulated by ATF:

Bump-fire stocks that do not fall within any of the classifications for firearm contained in Federal law may only be classified as firearm components. Stocks of this type are not subject to the provisions of Federal firearm statutes. Therefore, ATF does not have the authority to restrict their lawful possession, use, or transfer.

The 2013 letter from Marianos was in line with a 2010 letter sent to bump stock manufacturer Slide Fire by John Spencer of the ATF's Firearms Technology Branch.

In early December, the DOJ and ATF announced that they were initiating a review of the legality of bump stocks. However, if bump stocks remain outside the ATF’s regulatory sphere, it would likely take an act of Congress to ban the accessory on a federal level (they are already banned in several states, including California, New Jersey, and Massachusetts).

On February 21, Trump talked about arming teachers. He later tweeted:

The president has also tweeted support for “Comprehensive Background Checks with an emphasis on Mental Health,” as well as raising the age at which civilians are allowed to purchase semi-automatic rifles.