He presumably had an FFL holder among his personal staff or Secret Service detail. From the Gun Control Act of 1968:
a) It shall be unlawful—
(1)for any person—
(A) except a licensed importer, licensed manufacturer, or licensed dealer, to engage in the business of importing, manufacturing, or dealing in firearms, or in the course of such business to ship, transport, or receive any firearm in interstate or foreign commerce
That would be a straw purchase, which is totally illegal.