A government big enough to give you everything you want is big enough to take it all away -- Ronald Reagan
With one election, a Congress and President may make it illegal to cross state lines with a weapon because they can -- and have -- done things like this ...
Title 18 U.S.C. §922(q)
(1) The Congress finds and declares that-
(A) crime, particularly crime involving drugs and guns, is a pervasive, nationwide problem;
(B) crime at the local level is exacerbated by the interstate movement of drugs, guns, and criminal gangs;
(C) firearms and ammunition move easily in interstate commerce and have been found in increasing numbers in and around schools, as documented in numerous hearings in both the Committee on the Judiciary [3] the House of Representatives and the Committee on the Judiciary of the Senate;
(D) in fact, even before the sale of a firearm, the gun, its component parts, ammunition, and the raw materials from which they are made have considerably moved in interstate commerce;
(E) while criminals freely move from State to State, ordinary citizens and foreign visitors may fear to travel to or through certain parts of the country due to concern about violent crime and gun violence, and parents may decline to send their children to school for the same reason;
(F) the occurrence of violent crime in school zones has resulted in a decline in the quality of education in our country;
(G) this decline in the quality of education has an adverse impact on interstate commerce and the foreign commerce of the United States;
(H) States, localities, and school systems find it almost impossible to handle gun-related crime by themselves-even States, localities, and school systems that have made strong efforts to prevent, detect, and punish gun-related crime find their efforts unavailing due in part to the failure or inability of other States or localities to take strong measures; and
(I) the Congress has the power, under the interstate commerce clause and other provisions of the Constitution, to enact measures to ensure the integrity and safety of the Nation’s schools by enactment of this subsection.
(2)
(A) It shall be unlawful for any individual knowingly to possess a firearm that has moved in or that otherwise affects interstate or foreign commerce at a place that the individual knows, or has reasonable cause to believe, is a school zone ...
Now change "school zone" to "shopping center", "highway", "park", "museum", "church", or "any thing that receives public funding".