I hate to say it but I tend to think of people who ride without helmets as not having a whole of brain to protect. In certain situations, I can see that helmets aren't really necessary but its just a good idea to always wear one.
When I was alot younger and way, way dumber, I'd ride a sport bike (yes, motorcycle) without a helmet regularly. I survived but would no way, no how ever do it again.
I don't support crucifying the president for not wearing a helmet but he should keep in mind that he's a role model. Plus, he's got a really important brain to keep intact because, much as I like Joe Biden, I don't want him running the country.