<<<Global pandemics have been going on since the dawn of time>>>
They have been going on for thousands of years, but no since the dawn of time.
<<<why do the Democrats blame Trump for not doing enough?>>>
Maybe because "Trump Fired the Entire U.S. Pandemic Response Chain of Command in 2018"
http://www.pensito.com/2020/02/08/trump-fired-the-entire-u-s-pandemic-response-chain-of-command-in-2018/
Maybe because Republicans blamed (and are still blaming) Obama for the way he handled the Ebola outbreak.
Maybe because some of the stupid things Trump has said about it.
Maybe because Trump appears to be most interested in controlling the political implications by doing things like banning CDC from openly discussing it.
Maybe because of the whistleblower who said US workers weren't ready for evacuees.
https://www.usatoday.com/story/news/nation/2020/02/28/coronavirus-whistleblower-complaint-prepared-covid-evacuees/4901176002/
I am not saying all the blame Trump has received is fair, but as president he will always get credit and blame he does not deserve.