Agreed that a random pharmacist, with unknown motivations, should be disclosing any of this. The doctor who prescribed the meds should be (a) encouraging the representative to resign; (b) disclosing it to a proper authority; (c) disclosing to the news media if nothing is done.
There have to be tradeoffs. If you still want privacy, have it, but then you get to stay just a normally wealthy, powerful person and can live out your days sipping mai tais on tropical beaches and doing hookers and blow every night, but not being put in charge of a military with the power to glass half the planet if it wanted to.
And if pharmacists choose to share what they know, wouldn't that drive people to get their prescriptions filled another way (fake IDs, assumed identities, black market, cross-border/mail-order) or just not get medicine for fear of a medical secret being announced?
A better alternative: We should stop electing people who are clearly having a hard time thinking.
It's an interesting question whether this is ethical. On the one hand, representative democracy requires competent representatives, and knowing they have cognitive impairment is really important information for the whole country. On the other hand, I absolutely don't trust a random pharmacist to decide which personal, extremely sensitive information is important enough that they should be able to non-consensually share it.