Closing borders would probably have had zero effect because covid was already raging in the USA. I caught it back in Feb 2020 along with pretty much every other person I know. That was a good month before covid-hysteria kicked into high-gear. In fact, it's likely that the USA was well on the way to heard immunity. Locking everything down was just stupid especially for a disease that only kills fat-fucks and people who are basically already on the way out.