The reason you took anti-milarial drugs, and probably a shot for Yellow Fever and perhaps Dengue Fever and cholera is to allow your body to make anti-bodies to fight off these diseases against which you have no natural immunity. They don't cure the diseases, they just allow you body to fight them off. You usually have to take them 2 weeks before you go, to allow time to work within your body. (as you can tell, I have been through this on trips to Pakistan and other savory locations).
I have not read anywhere that Hydro is helping anyone develop antibodies against COVID. If it were drug companies that were claiming it ineffective as a preventative, I would be skeptical. But a host of Drs, scientists and researchers are saying that we need a vaccine. If any one of them had through Hydro was a cure or a dependable preventive medicine, don't you think they would love the opportunity to save global health with an already proven drug?
I personally think the reason that Trump is taking the medicine, is because he touted it as a game changer - and if he doesn't get COVID, for any reason, he'll be claiming he was right. You have to admit that he doesn't like to be wrong about anything.