There are ways to identify many. For example, we started restricting people with domestic abuse convictions but a court has stepped in and said that for that circuit, no.
A recent ruling by the 5th Circuit Court of Appeals said the Second Amendment allows people accused of domestic abuse to have guns. The ruling applies only to the 5th District, but advocates said there could be ramifications nationwide.
news.wttw.com
I would also suggest people convicted of cruelty to animals.
I would suggest people who commit certain crimes while carrying a gun. For example, these smash-and-grabs may not be felonies, but if one is stupid enough to have a gun on them while carrying it out, they are a danger.
This MSU guy, he was accused of firing a gun out his back door. Maybe in nowhere, not a problem. In a city, he's a danger. Just about any reckless behavior with a weapon qualifies. If someone doesn't take the danger of a gun seriously, they are dangerous. We follow that rule with drivers.
Reports of credible threats and intimidation should be strongly considered. If someone tells their neighbor they will kill them, we should take them at their word.