The second amendment is short and simply put:
“A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.”
Inspired by this, I propose that the national government should require states to create periodic, military-like training camps to ensure that citizens who own or operate firearms (at least assault and high capacity firearms) are ready to protect the USA; if the state wants to allow their citizens to own such firearms, of course.
This should be state-run with national minimal requirements so that states can base their training on state-specific requirements (e.g. geographical tactics). The periodic training will ensure that all gun owners do not pose a threat to the well-being of citizens.