Watching the show today on gun control, I thought of a possible solution. Like US Passports, we should apply for a license to purchase a gun, with an expiration date. Renew the license after a certain time, to get current background checks. That would need pre-planning and stop the angry person wanting to do harm right away. Waiting for the license might simmer that person from doing harm.
The ATF would have a section of employees to handle the transaction. Charge the people in applying to pay for the service. The NRA should be happy with this too. This will cover the gun show. They show their license.