CentralOklahoma Said - "In reality, police officers in the United States are the most looked into and evaluated persons around."

Yes/No/Maybe.

Depends on where you are and when the LEO was brought on the force. It sounds like major cities and districts are spending considerable amounts of time, money and effort to weed out unstable people before they get in. In part for reasons of liability. One unstable cop can do a lot of physical, mental, financial and reputational damage.

They also tend to spend resources to help keep those in at least fairly sane. Not that many LEOs take advantage of these services for fear of appearing weak or unstable. This might be changing over time but IMO a lot of LEOs are still self medicating with macho bluster and/or a half a bottle of scotch after every shift.

It is a high stress job that wears over time and the results, even short of homicide, are not pretty. The rates of divorce, suicide, domestic violence and alcoholism are telling. This stress also reinforces the 'police culture' where cops hang with cops and marry cops and get farther and farther away from the people they enforce the law on every day. Which increases stress, isolation and detachment.

Smaller and poorer districts just don't have the funds to do much screening and treatment to keep people level can be even harder to find. Some districts pay so little and are under such tight political control they have to relax the standards quite a bit. They can't afford to be too selective.

That said I wonder about the testing that is done. There is testing and testing. Spend enough money, often thousands of dollars and many hours per person, for specialists in mental health and psychology to do detail analysis and you can weed out the almost all the folks likely to fragment and cause casualties.

On the extreme other end get the local school nurse to give a 10 question standardized mental health exam she picked off the internet and it takes ten minutes and cost $5 per person. The question is not only what you can afford. It has to do with the intention of the testing. Is it to really weed out the unstable? Or is it intended to document an effort to weed out the unstable with an eye toward meeting standards to get cheaper insurance and avoiding liability. While crossing fingers and hoping the worse doesn't happen.