Wouldn't that hypothesis predict that if California didn't suffer, Trump was nice to Cali?
Don't see that.
Notice also the acclaim that greeted the travel ban:
https://www.nytimes.com/2020/03/12/world/europe/europe-coronavirus-travel-ban.html
In his address from the Oval Office on Wednesday, Mr. Trump pointedly described the source of the epidemic as a foreign virus and criticized the European Union for having failed to take the same precautions as he had in restricting travel from China, the source of the outbreak.
As a result, a large number of new clusters in the United States were seeded by travelers from Europe, Mr. Trump said.
In fact, Europe has not been a major source of known infections so far in the United States.
It goes on to make fairly clear that the NYT considered the ban not to be too late but to be completely offensive and wrong. In other words, the opposite of what the NYT now says it said. (It's like the media tweets from late January saying that the novel coronavirus was being contained and wasn't a problem here, so be more worried about the flu ... they vanished because they don't fit the current reality).
DU was mixed. Some said it pointless because it was too late, some were more upset at the exemptions (leaving whether the ban itself was a good idea), some objected to offending Europe so there shouldn't have been a ban.
In short, the same blather we heard in late January when the ban on travel from China was imposed. It won't work in principle, it won't work because there are loopholes, it won't work because too late, or it's simply offensive. It's only in retrospect that the mistakes we make vanish from the pages of history and we've always been right.