The "all" part is, from what I can tell, considerably less important than the "not just banning direct travel" part... the model assumed that only most of the t

The "all" part is, from what I can tell, considerably less important than the "not just banning direct travel" part... the model assumed that only most of the travel from China was stopped, and that was still enough to cause a huge delay in the outbreak. It is far better to have 30 aircraft from China landing in San Francisco than to have 30 aircrafts' worth of travellers originally China spread out across hundreds of aircraft from other destinations, such that you have no idea who the travellers are, where they are, they could be spreading it to completely unrelated travellers from different destinations - which is what Italy effectively did. "This is either ignorance or an intentional lie. Which is it?" Joe Biden literally got up on stage and claimed that the travel bans made the US outbreak worse - and was quoted in the mainstream media as doing so. "They opposed that it was the singular action taken during a very dangerous period. That quarantines or even tracing weren't put in effect. Etc." Errrm... that's not actually true though. There was definitely plenty of contact tracing in the US, it just didn't get a huge amount of media coverage. Also, I can't imagine locking up US citizens of Chinese origin en masse going down well at the time when it would actually have to have been done... especially since it ultimately wouldn't have helped all that much. The contact tracing and other indications, like genetic analysis of the Covid strains which spread in the US, suggest that the measures the US took were effective enough that spread from China isn't what ultimately ended up causing their big outbreaks. Not taking measures against spread from Italy when that country was reporting zero cases is probably what did it, and realistically that wasn't going to happen.