I thought this too. At first. But consider....
1. Typhus and other communicable diseases could spread to the rest of the US. California could infect the rest of the country. We should quarantine that state. Refuse to permit anyone from leaving it. Unless and until they provide a clean Bill of Health.
2. Trump is pissing off elected officials in California who are too freaking stupid (or afraid) to acknowlege the problems their socialism has created. And this is his way of giving them the Finger.
California is broke. They can’t do anything because they have no money to do anything.