The point is that its being used globally as a potential treatment and isnt just some Trump conspiracy theory,
The first news of the treatment came from China in the first place with their reporting they were using it to successfully treat infected.
Studies coming from china where inconclusive.
https://www.contagionlive.com/news/results-from-a-controlled-trial-of-hydroxychloroquine-for-covid19
Ten days later:
https://www.biospace.com/article/china-clinical-trial-says-malaria-drug-doesn-t-help-covid-19/
(Just the first links found via google. Sources not vetted.)
The problem basically was, that he was briefed on the first one (probably), then 'upgraded' the results of the study in terms of viability, and then stuck to that script - for too long, while the rest of the world already was informed, that results on hydroxychloroquine were inconclusive. (Thats the 'what the heck is he doing' part.)
Also there have been two additional issues with that recommendation, first hydroxychloroquine, when taken in doses that turn out to be too high is poisonous, and people (- even in the US) died from taking it (clinical trials), second, that patients with Lupus - who rely on that drug as treatment suddenly werent able to get it, because people rushed to get prescriptions based on - in non scientific lingo - a theory, thats was still in the process of being evaluated. While the POTUS told people, go get it "what do you have to loose". While not having ramped up production beforehand.
Thats the entire argument.
edit: From a PR standpoint, at least that brought 'hope' to some people ('there is a potential cure that already exists'), at a time, when arguably it was needed.