I used to work with guys that had security clearance (not sure what level) but I would often hit on areas where they would say “I can’t talk about that,” and would cite their oath to protect that data no matter who they personally trusted. I never took it personally and in fact thought it was pretty cool I would ever come in contact with potentially sensitive information to require someone to inform me of it. I think at a minimum a potential President needs to have that level of respect for secret information.
This is one of the downsides to having a civilian as commander in chief.
I would personally prefer that a candidate would have to have served in the military prior to running for the office.
That would be no panacea, but at least then a person would actually understand taking as well as giving orders, and would understand the necessity and importance of classified materials.
It can also be the case where these peeps were subject to random polygraphs to ensure their silence about the job. I know.