Fauci Wrong? A Mini on the Nature of Science.
Science is not static it is ever changing and changeable.
Scientific knowledge is gained through Scientific Inquiry - asking questions, observation, experimentation, data collection, interpreting and drawing conclusions.

Doing these processes results in Scientists to build a body of evidence based Scientific Knowledge. But the body of knowledge is not set in stone. It is changeable. Our understanding of the nature of Earth changes as scientists observed new evidence.

With new evidence and interpretation, newer ideas replace or supplement old ideas.
For example, the world was once thought to be flat, and now we know that it is round.
This is the Nature of Science.

Science is not satisfied with current ideas. Rather it strives to constantly improve, clarify, and supplant old “truths” with new ones.

When Covid-19 first showed up in this country, Not much was known about it. We knew its Genetic sequence,

that it was deadly and that it was transmitted by contact. This information indicated that wearing masks by the general population was not necessary. So knowing that, and that they were in short supply, masks were used only by first responders and hospital workers.

Now with all of this, Scientist around the world started Investigating Covitid-19. Fairly quickly in early April it was discovered that this virus was also transmitted through the air. Once this was known, the use of Cloth masks was recommended.
This is how science is done.

Finally, came the search for treatments for Covid.
Stories out of China talked about a medication named Hydroxychloroquine. This drug was seized on by people as a ray of hope. The FDA authorized compassionate use for it with Covid patients. Through this Fauci urged caution.

He urged the caution because of the known side affects of this drug and because there was no scientific evidence that it had any affect or benefit. He urged that its use be limited until it went through the FDA process of double blind testing.

The FDA and other around the world started investigating the affect of this drug on Covid. Data was collected and analyzed. It was a good thing that Fauci recommended the testing too. only part was through the trials, data showed the drug had no affect on the virus and

it showed major deadly side effects for the patient. July 1, 2020 Update:

A summary of the FDA review of safety issues with the use of hydroxychloroquine and chloroquine to treat hospitalized patients with COVID-19 is now available.

This includes reports of serious heart rhythm problems and other safety issues, including blood and lymph system disorders, kidney injuries, and liver problems and failure. Article found at: https://www.fda.gov/drugs/drug-safety-and-availability/fda-cautions-against-use-hydroxychloroquine-or-chloroquine-covid-19-outside-hospital-setting-or