There is a lot of controversy since the Orlando shooting regarding the availability of weapons for terrorists and other mass shooters in the US.
One idea being pushed is to take away the rights to buy guys for anyone on the no fly list.
However, there are valid criticisms to this plan, given that the no-fly list is full of both false positives and common names. Laughably, even Senator Ted Kennedy had problems flying because the government had been told that some terrorists were going to fly under the name "T. Kennedy", and that prevented all Ted Kennedys from flying without intense questioning (even the Senator whose legal name was Edward!)
It amazes me that the no-fly list isn't attached to BOTH name and birthdate, so these mistakes don't happen, but apparently this is very common.
However, it's also ridiculous that a suspected terrorists like Omar Mateen was able to purchase high-powered weaponry without anyone blinking an eye. We've also had situations of mentally ill people managing to purchase firearms, and the committing mass shootings.
There is no easy solution to this.
However, I think that one solution would involve better communication between agencies.
If someone attempts to purchase weapons, and are on any sort of terror watch list, the organization which put them on the list should be contacted immediately, and that person should be investgated. While the investigation is occurring, the person's right to firearms should be frozen, but not irrevocably denied. At the conclusion of the investigation, it would then be determined if the person should be allowed to purchase firearms or if they should be permanently banned from it (or perhaps imprisoned for a planned terror plot).
Similarly, anyone institutionalized in the past for mental illness should be required to get a licensed psychologist or psychiatrist's approval to purchase weapons -- at least for the first purchase since being institutionalized.
Finally, the gun show loophole, allowing people to avoid background checks, should be eliminated.
We must take action to at least make it more difficult for terrorists and mentally ill people to obtain powerful weaponry to commit mass murder. These measures will not completely stop mass shootings, and even complete gun control (which I am very against) would also fail to end mass killings. Remember, the Boston Marathon mass killing did not involve any guns.
However, right now it is too easy for guys like Omar Mateen to obtain weapons that allow them to quickly murder 50 people. There has to be at least some roadblock to this sort of thing.