He's an easy target, of course, but I really believe that Trump has to take much of the blame for recent events in the States: even by his standards, he's handled this abysmally.
Firing his Pandemic Response Team to fund tax cuts; reducing funding for the CDC; and, until very recently, insisting it was all a hoax created by the media and the Democrats. It was inevitable that when things finally did go pear-shaped, Wall St would panic because they had been left in the dark and completely unprepared.
Now that the first death in the US has been announced (and in Washington State too, so a great big to all our GaGa friends), I think it's understandable that when Wall St reopens on Monday, many will think about how the US response is now being led by a science-denying creationist who believes smoking doesn't kill and condoms give "very poor" protection against STDs, and come to the conclusion that things are likely to get a whole lot worse before they get better...