It's not about shielding or not shielding China from blame, it's about:
A. Making sure people of Asian descent who did nothing wrong aren't harmed.
B. Not allowing our leaders who have been completely in adequate to hide behind blaming it on China.
Why shouldn't they?
It's like someone having a truck of cow manure tipped onto them and instead of blaming the person who tipped it, instead blaming the person it got tipped on because he couldn't clean it up fast enough.
There's a weird consistent attempt to not blame China for this because it's more convenient to lay it politically on Johnson and Trumps door. I just don't get how people don't see the bigger picture.
None of this happened because of Boris Johnson or Donald Trump. That's an inconvenient truth for some. Their inaction and incompetence compounded the issue, but it wasn't they themselves that caused it in the first instance.
So when Trump says "blame China", it'd be nice if the media actually did, because they could then at least turn round and say "... but after the fact, your decision to X, Y and Z didn't help mitigate the damage" etc. without being disingenuous and using the situation solely to go on the attack.