The thing that is so grating is that even if Trump's claims about the WHO are right then quitting it is arguably the worst response to that. The US is one of WHO's biggest funders and, it follows, has the potential to be quite influential. When a huge player in an organisation quits they abandon all possible claims to influence and all attempts to actually solve the problem.
What, I wonder, is Trump's proposed replacement? It is pretty clear and obvious that a global health threat requires a global health organisation to respond to it, so I hope he has a plan. Except, of course, he doesn't. Quitting the WHO is a clear and obvious distraction technique, deflecting attention from the US's own response, which, despite a promising start*, simply stalled and has led the US to 100,000+ deaths with no real sign that they are anywhere near the end of the crisis yet.
Trump does enjoy boasting about how quick he was to cut off travel from China. This is true. What he seems to forget is that this on its own was never going to stop the spread of Covid-19, merely slow it down and buy time. What did the US do with that time? Nowhere near enough. Not even close. There's no point in boasting about a half-finished job. Sadly, Trump seemed incapable of seeing that he had to follow up the early action with more preparatory measures that came far too late.