

Assuming you mean in the US, there is a national system called NICS that basically has the FBI run a background check. Some states have additional systems to augment that.
The conditions that get you put into the “no” list are things like committing a felony, domestic violence, drug use, etc. Being committed (against their will) to a mental institution is on that list. A mental institution would have to report you with evidence to get you added to the list. Potentially, he could ask his psychiatrist to do that for him. It may not be an option, but if you brother is worried himself, that is good evidence, I think.
When you buy a gun, you have to check boxes on a form to say you aren’t a felon, addicted to drugs, a fugitive, etc. They can check the felon and fugitive part, so if you lie, you get in big trouble. Drugs, though, they obviously dont have a list, so really it’s just a way to add penalties if they can later prove that you lied (e.g., hunter biden). You couldn’t just do a drug and automatically pop onto a list.



Yeah, this is really the answer. Over and over and over again, it’s clear that the policy of his regime has always been to “flood the zone”.
Every single week, they do something unique and so heinous that it would have ended any prior administration. They can keep things from sticking by just continuing to do stuff like that and get popular focus on a new thing. The people that should be able to keep them accountable legally are similarly overwhelmed.
Greenland was probably never a serious thing for the regime, it just had to serve a purpose of keeping their opponents busy. It’s the political equivalent of a gish gallop.