18 USC § 922
(d)It shall be unlawful for any person to sell or otherwise dispose of any firearm or ammunition to any person knowing or having reasonable cause to believe that such person, including as a juvenile—
(1)
is under indictment for, or has been convicted in any court of, a crime punishable by imprisonment for a term exceeding one year;
(n)
It shall be unlawful for any person who is under indictment for a crime punishable by imprisonment for a term exceeding one year to ship or transport in interstate or foreign commerce any firearm or ammunition or receive any firearm or ammunition which has been shipped or transported in interstate or foreign commerce.
As I read it, the gunshop owner broke the law if they gave or sold it to Trump.
But Trump broke the law only if the gun were manufactured out of state. Again, gift or sale is irrelevant.
I assume the interstate commerce part derives from constraints on federal power in the constitution, but I don’t understand why that qualification applies only to the buyer/receiver.