Midterms are definitely important as far as putting some brakes on the crazy train.
There was plenty the Dems didn't do that they should have done when they had their chance, but when you look at something like vaccine roll out under Trump, the way it went once the Senate subcommittee on COVID was formed, was not the way Trump was planning.
Before Dems got involved, Trump had already been making plans to give a private pharma company government contracts. As bad as COVID in 2020 was, it definitely could have been a lot worse if Trump had been allowed to run wild.
Here's a nonpaywalled version
TLDR, he was planning on completely privatizing and patenting a vaccine, that wouldn't be affordable to the majority of the country. Shit would have been horrific.
Not to mention the company he would have contracted with ended up having a lot of quality deficits due to bad manufacturing/production issues. So the vaccine they would have made, which would have been insanely expensive, also would have been dangerous bc of the shitty quality.
Democratic oversight after the midterms is the only reason why we had the private-public rollout with the NIH handling safety and research and Moderna and Pfizer handling rollout.
This is also why Trump has taken away the NIH funding given to Moderna by the Biden administration for an up to date bird flu vaccine, and why he is so set on destroying public funding in science and safety oversight.