Biden in February:

Alexis apparently thought this was a great idea and bought himself a shotgun last week:

Via WSJ:

The early investigation indicates that Aaron Alexis legally bought a shotgun at a Lorton, Va., firearms dealer last week.

The law allows a buyer to purchase a long gun – which is a rifle or shotgun – without being a resident of the state where the firearm is bought.

The question then falls to whether Mr. Alexis was in any prohibited category that would have prevented him from buying a firearm.