The soup of conspiracy mongering about the covid-19 pandemic has never truly settled on a clear story. Even as the virus began spreading internationally, reactions ranged from claims that China was exaggerating the numbers of people infected to China was hiding the ‘true’ scale of infection. The common theme with conspiratorial thinking is that genuine doubt, genuine ignorance and genuine shifts in opinion about a novel situation are actually examples of deceit. There is a paradoxical relationship with authority and expertise in any conspiracy theory as the claims of deception always imply that the authorities genuinely do know a lot more about the true state of affairs than everybody else but are lying about it.
The most recent iteration of covid conspiracy-mongering is the ‘Plandemic’ conspiracy video which has sprouted out of anti-vaccine conspiracies. You can read more about it here https://www.theguardian.com/commentisfree/2020/may/14/plandemic-movie-discredited-dr-doctor-judy-mikovits-how-debunked-conspiracy-theory-film-went-viral but there is also a good analysis of conspiracy-theory thinking which uses it as an example here https://theconversation.com/coronavirus-plandemic-and-the-seven-traits-of-conspiratorial-thinking-138483. The conspiracy is being promoted among some sections of the media in the usual just-asking-questions/exploring-the-controversy way:
“Local television stations owned by the Sinclair Broadcast Group are set to air a conspiracy theory over the weekend that suggests Dr. Anthony Fauci, the nation’s top expert on infectious diseases, was responsible for the creation of the coronavirus.The baseless conspiracy theory is set to air on stations across the country in a segment during the program “America This Week” hosted by Eric Bolling. The show, which is posted online before it is broadcast over the weekend, is distributed to Sinclair Broadcast Group’s network of local television stations, one of the largest in the country. A survey by Pew Research Group earlier this year showed that local news was a vital source of information on the coronavirus for many Americans, and more trusted than the media overall.”https://edition.cnn.com/2020/07/24/media/sinclair-fauci-conspiracy-bolling/index.html
What the various conspiracy theories have in common is a belief that pandemic fears and public health measures are specifically a plot against Donald Trump. The details vary (or even contradict each other) but they aim to support a motive for the imagined conspiracy i.e. that the ‘ruling classes’ have manufactured pandemic fears as a way to undermine Donald Trump. To support this idea conspiracy-theorists point to pre-pandemic articles discussing how Trump might cope with a pandemic (e.g. this one by Ed Yong in 2016 https://www.theatlantic.com/science/archive/2016/12/outbreaks-trump-disease-epidemic-ebola/511127/ ) as evidence that people were ‘planning’ to use pandemic fears against Trump.
Ironically, across the world many political leaders have gained popular support as a consequence of the pandemic (https://www.washingtonpost.com/world/2020/05/13/some-world-leaders-popularity-grows-along-with-coronavirus-case-numbers/ ). This pandemic poll-boost has helped politicians both on the left and right and isn’t tied to any particular policy measure nor even whether the covid-19 response was particularly successful. Clear messaging and decisive policy appear to be the main factors but even the shambolic Boris Johnson gained an initial popularity boost (although he eventually squandered it https://www.theguardian.com/politics/2020/jun/14/poll-uk-government-losing-public-approval-over-handling-of-virus ).
The reality of natural disasters, including pandemics, is that they can often boost the standing of national leaders. Nor is it difficult to gain support because it is mainly a halo effect from the leader being seen in the company of competent people doing their jobs at a time when people will naturally hope for national unity. It actually takes some effort to mess up. Notably, the Australian Prime Minister, Scott Morrison, managed to do this during the 2019/20 bushfire crisis leading to a rapid plummet in support and humiliating scenes of firefighters refusing to shake his hand. Conversely, Morrison saw his poll numbers boosted during the pandemic, mainly by not repeating the same basic errors he had a few months earlier.
In short, natural disasters are more likely to boost a national leader than undermine them. As a plot against Trump, a pandemic would be a terrible idea: all Trump would need to do is look presidential, let experts speak and pat them on the back. Of course, there is a counter-argument here. A pandemic may well be an actually electoral boost for most politicians but specifically a problem for Trump. As we have seen, Trump has spectacularly failed but this was entirely due to his own incompetence and the incompetence of his cronies. Even so, in late March, the pandemic led to Trump’s approval numbers steadily improving, only to be undermined by Trump’s inability to handle a crisis.
In short, as a plot against Trump, a pandemic would only undermine Trump’s popularity if Trump was actually a uniquely bad president. Of course, he is actually a uniquely bad president, so I guess that is one thing the conspiracy theories have going for them.
 Apparently Sinclair media have since changed their plans https://twitter.com/WeAreSinclair/status/1287110687093714944