The step is incremental, and the Justice Department still must go through a lengthy process to make the proposed regulation a reality. Bump stocks, which enable guns to fire like automatic weapons, were not used in that attack - they were used in last year's Las Vegas massacre - but have since become a focal point in the gun control debate.
"President Trump is absolutely committed to ensuring the safety and security of every American and he has directed us to propose a regulation addressing bump stocks", Attorney General Jeff Sessions said in a statement.
In a notice submitted for approval to the Office of Management and Budget, the DoJ proposed that bump stocks be included in the definition of "machine gun" in the 1934 National Firearms Act.
But the step is tangible evidence that the department is working toward regulating the devices, however gradual that work might be.
Trump had indicated two days ago that the paperwork for a ban on bump stocks was almost done.
He would have to complete a similar public comment process were the Office of Management and Budget to approve the proposed regulation. But, this new proposal would expand the definition of the term "machinegun" to include weapons modified by bump stocks. This would mean the possession, sale and manufacture of the devices are prohibited under federal law, which largely bans automatic weapons.
A bump stock is an aftermarket modification a rifle owner can install that allows a semi-automatic firing mechanism to mimic rapid firing of a fully automatic machinegun. The shooter placed bump stocks on several of the rifles he used in the attack, though it is not clear how numerous more than 1,000 rounds he fired came from those guns.
Because of the department's continued insistence that it cannot regulate bump stocks, the ATF's current reversal declaring the devices illegal could pave the way for manufacturers to challenge the new ruling in court, CBS News noted.
Opting for a plan the administration officials described as "pragmatic", Trump backs legislation proposed in Congress aimed at providing more data for the background check system - a database of people who are not legally allowed to buy guns.
Less than a month after the deadly shooting at Marjory Stoneman Douglas High School, Florida Gov. Rick Scott (R) on March 9 signed a gun control bill into law.