Amanda Marcotte is exactly right. Trump’s “Chinese virus” comment is a deliberate troll (as well as red meat for his deplorable racist base). Its purpose is to get us talking about his racism instead of his incompetence. That way, he (and his enablers) can turn the conversation to a discussion of when a racist comment is not a racist comment and exactly how it’s not racist. The conversation then just drops far, far down the rabbit hole and the real issue — Trump’s total incompetence — is lost.
The appropriate response is to (1) forcefully denounce the racism but (2) ignore efforts by the right to make racism the topic, and then (3) go back immediately to the topic of Trump’s thorough unfitness for office.
In short, acknowledge his racism, but don’t take the bait. The real subject is that Trump has absolutely no business being president. His racism is central to that, of course, but the point is to get him out of there as soon as possible.