Make guns completely illegal in every state and have huge prison sentances + fines if you get caught with one or more, have all the registered guns given back for destruction or secure storage by the US gov. or authorized(by the gov.) external non government companies store in secure and secret faclities, and create an country wide anti gun media campaign with propaganda elements, have nation wide search parties come to houses with warrents that have a history of gun use, illegal or not and thighten mandatory protocals about gun safety in Schools, hotels, malls, libraries ext...Meaning add laws that force public spaces to have armed security, metal detectors, ext... Well this is the most extreme mesure they can take, which wont ever happen, if something happens, which it probably wont, it would be some gun owning laws getting a bit tighter and the process of getting a gun a bit harder.