Some portion of Trump’s downturn is the fact that his base is getting impatient with the re-open. His initial statement of 4/12, then 4/30, then deference to the governors based on vague CDC guidelines is wearing on people. The important thing is to get the economy going as quickly as possible and then these numbers change. I don’t completely discount the findings.
As always add at least 10 points to Trump due to the silent Trump supporter. Plus there seems to be an a large number of undecideds who once they actually hear from Biden in person will run the other way.