This is difficult to write about and think about because the politics around it are completely warped. But I will try.
Republicans hate Fauci because:
1) Fauci insisted COVID-19 was a serious emergency that demanded serious measures including lockdowns and masking. And sometimes Republicans believe that not only were mRNA vaccines ineffective against the the virus, they caused all the excess deaths from a virus that otherwise would merely have been a mild flu. Republicans are wrong about these things.
2) Some Republicans think Fauci was responsible for the creation of the very deadly COVID-19 pandemic (which contradicts the first part, so many Republicans don't get this far). There may be some truth here because it is quite possible that Fauci helped set the ball in motion which ultimately led to COVID-19.
Democrats love Fauci because:
1) Fauci insisted that COVID-19 was serious (it was, of course) and demanded serious measures like masking and lockdowns (it did). Democrats are entirely correct about this but often fail to see the issues in points 2 and 3.
2) Fauci epitomizes "Science" (but "science" is also people with self-interests and blind spots, and science is sometimes wrong). That Democrats often reflexively side with Science, Medicine, and Law arises from a bias towards the PMC. All these things are best understood critically. (But this does not mean falling in line with cranks and charlatans either, we must be even more critical of them.)
3) The belief that there is no "scientific" reason to believe the Lab Leak Hypothesis (but the Lab Leak Hypothesis has not been disproven either, despite great efforts to do so, and many serious people believe it. Fauci himself initially believed that the Wuhan Meat Market was only an "amplifier" of the pandemic which originated elsewhere, and Fauci this day continues to admit that that it is not impossible that the pandemic originated from a "lab leak"...which meant that someone in a lab first caught the disease from GOF boosted specimens they were working on).
Given that we just had a Senate Hearing in which Fauci refused to answer 100 questions about COVID-19 it might be interesting to see what all of those questions were. But instead, the media and every source I can find is more interested in the politics of Fauci invoking the Fifth Ammendment when he was pardoned by Biden for activities starting in 2014. I have not even found (yet) the questions asked in official Senate documents released to the public.
COVID-19 ORIGINS
But starting in 2014, the NIH funded the EcoHealth alliance to study viruses at the Wuhan Institute of Virology (WIV). This appears to have been to evade the ban on GOF. The research in Wuhan continued despite the ban up to the origins of COVID-19 and possibly beyond.
Because this research was being done in China, it was not affected by the ban on doing this research in the US, and also the later "stricter oversight" applied to doing it in the US.
It is known that WIV was doing research on Coronaviruses that could be characterized as GOF research (though perhaps not by certain definitions of that) in a BSL-2 laboratory (inadequate for the task and outside US oversight) at the time COVID-19 was released. Therefore, a lab leak from WIV remains a highly plausible origin of COVID-19, and several US intelligence agencies (FBI, DOE, and CIA) concluded as early as 2021 (with low to medium confidence) that COVID-19 most likely originated from a lab leak and they maintain these conclusions to this day. The Lab Leak Hypothesis is not a crazy "Conspiracy Theory" believed only by kooks no matter how much some media and scientists say that it is.
We don't actually have enough detail to prove the Lab Leak Hypothesis because China has never allowed anyone else to see critical information about what WIV was doing in 2019, which itself is suspicious, because if this information were not incriminating they would have no reason to hide anything. It is also known that several people involved in this research at WIV got seriously ill around the time in question.
Some, typically MAGA, believe that COVID-19 was a Chinese plot, but US involvement in funding similar research in Wuhan somewhat weakens that idea, as well as the fact that China itself was the first to have to deal with COVID-19 and lost lives and considerable resources because of it. There have been others suggesting it was a US plot, and COVID-19 was simply "planted" in Wuhan to disrupt China, but once again the US suffered even more from COVID-19 so if it was a plot it was surely very inept. These ideas that COVID-19 was a plot are examples of crazy conspiracy theories, but they should not be confused with the Lab Leak Hypothesis.
There have been panels of scientists (mostly virologists with vested interests at hand) who concluded the COVID-19 origin was not likely lab leak based on technical details about the virus and the Wuhan Meat Market, but those conclusions are not air tight, so a lab leak still remains plausible. It should be noted that no "smoking gun" was ever found at the Meat Market or elsewhere. No evidence of COVID-19 has ever been found in the wild, as has sometimes been done before with other pandemics. All we know is that people in Wuhan were apparently the first to get it (though we can't be entirely sure of that either). And, perhaps not coincidentally, Wuhan had the WIV which had been doing GOF research on coronaviruses. That is a remarkable fact, actually. Meanwhile, the animals alleged (but never found) to be part of a zoonotic transfer were a considerable distance away. Why did COVID-19 not start there, among the people living near or capturing these animals?
Early on in the investigation of the origins of COVID-19, some scientists claimed that the structure of the virus could not have developed naturally, it clearly looked like a result of GOF genetic splicing. Much of the research claiming zoonotic origin of COVID debunks that notion. But it does not prove that COVID could not have been created by GOF research.
Fauci denies that this particular Coronavirus research being done at WIV in 2019 was funded by NIH, and he is correct. However, previous research of that nature WAS funded by NIH through EcoHealth Alliance. What WIV was likely doing in 2019 (and this is what Jeffrey Sachs, who led one task force investigating COVID origins said in 2021) was unfunded research in the anticipation of funding. Like Dr Sachs, I have worked in science and I know this is how labs operate. A cynic could even believe the real research is the "unfunded research," and when the funding finally arrives that research is now virtually complete, and the funding is then mainly used to start research seeking the next funding opportunity, in effect being the "unfunded research" for that. Sachs himself, after leading a panel of scientists investigating COVID origins, came to believe in the Lab Leak hypothesis and has said so in papers and interviews. He looks primarily to the fact that China has refused to give the details on the research being done at WIV in 2019 as evidence of a coverup. Those who believe in Zoonotic Transfer have the sort of racist view that the Chinese are always this way.
Funded or not, the research which may have originated COVID-19 was done in a lab that had previously received NIH funding for doing very similar research, and they might have anticipated funding getting funding for that research too eventually. If it hadn't been for the initial NIH funding, they might not have been doing that kind of research.
Because of the risks, and the ban on GOF research in the US, the NIH should not have been funding EcoHealth alliance to do the GOF research in China. Fauci was head of the Infectious Diseases Institute of NIH, and he also reportedly had direct personal involvement in getting EcoHealth funded to do this research in contravention of the US ban. Therefore Fauci himself helped initiate the research program which may have ultimately produced and leaked COVID-19. Because Biden pardoned Fauci for all his activities going back to 2014 Fauci cannot be prosecuted for this. He may have violated US laws, and, if the Lab Leak Hypothesis is true, he might bear considerable moral responsibility for COVID-19.
If I may, let me add one more personal observation. People who are paranoid about germs do not go into research in Virology. People who are paranoid about germs avoid going near Virology Departments. Virologists tend to downplay the risks of the research they are sometimes doing, as they would almost have to do in order to do this research, and overplay the benefits. It is not clear to this day that GOF research on viruses has done anything useful. Vaccines, for example, are not devised using GOF research. I first heard about GOF research in 2011 (in a Virology Department presentation btw) and I was immediately scared about it. I've also toured a BSL-4 lab (very impressive) and a BSL-2 lab (not where I'd want to work on anything dangerous).
Pandemic Handling
Finally there is one small issue about pandemic handling that also involves Fauci, but has been so warped by the politics we can't get straight answers. Many Republicans and especially MAGA are still convinced today that masks are useless (often along with the unfounded notion that COVID-19 was fake, and the mRNA Covid vaccines caused all the deaths). This is bad, very bad. But even Trump himself got the vaccine which his Operation Warpspeed had helped create more effectively than otherwise. Though Democrats often dispute that Operation Warpspeed made the vaccine available more quickly, it specifically helped fund development of the Moderna mRNA vaccine, which proved to be among the most effective or even the most effective, and if the independently funded Pfizer vaccine work had failed to be useful it might have taken far longer to get a useful vaccine without the Moderna one. As it turned out, both vaccines became available at about the same time, sometimes giving the public a choice, and most likely cranking out shots more quickly than if it had been left to Pfizer alone.
Early in the pandemic, Fauci (and others) emphasized the importance of hand washing (which is relatively unimportant in the transmission of COVID-19 and many other infectious respiratory diseases) and did not tell the public that masking was a good idea. This was not good. (This attitude was and still is common among doctors--including my own PCP at the time--and even in hospitals.) Later, when it was finally advised that masking was important, the public was prevented from getting highly effective N95 masks and instead told to use simple cloth masks, which are not highly effective and generally protect others more than oneself. I see this as a grave error. Instead, all measures possible should have been taken to ensure an adequate supply of N95 masks both for professionals and the general public. There should have been an earlier Operation Warp Speed for making N95 masks as well as vaccines, and/or lifting sanctions to enable buying them from China. I myself would never have appreciated N95 masks unless I had a friend touting them and giving some away. Even today people wear lesser masks without much thought. The government now recommends people use N95 masks in risky situations but has never made a big deal about it, as big as the deal to use cloth masks was during the peak days of COVID-19, so many people have never heard about it.