So Australian/New Zealand restrictions coulda been reproduced elsewhere in the world (we know that because of China and Vietnam, because neither is an island). It would have been, however, as we see also from China and Vietnam, much more problematic in the United States because:
-Trump was President. He realized within 2 months he had been played by Birx. He wanted to reverse course (but was hamstrung in doing so without coming out before the election and admitting to everyone he was played)
-Unlike NZ and Australia, we were in season and COVID had already been circulating in the US for months and NY was already in a full outbreak when the trigger was pulled on lockdowns.
-The US border is much longer than Australia/New Zealand. Would have required a hard shut down of air travel abroad and massive policing of the southern border even to US citizen (unpalatable to the Democratic party). We would have had to treat the southern border like the Spanish treat Melilla and Trump couldn't even get his border wall done (assuming Canada would have gone along in a free north america zone).
-The first amendment. Would have required the suppression with force of the BLM protests when quarantine was broken.
-It would have required getting the courts to go along with shutting down travel between the states and cities despite the constitutional protections for interstate travel. Florida had to back down when NY complained about the DeSantis embargo on New Yorkers coming to the state.
-Federalism. Would have required the federal government imposing its will on the states going so far as to remove DeSantis and Noem from power.
-Would have required the federal government to impose the lockdowns on an armed citizenry a large segment was opposed (who by koinkey dink also controlled the guns), not to mention a large enforcement regime where neighbors notified on neighbors for leaving their houses. The courts would have had to have gone along with.
-Would have required the federal government to do a broader shutdown of essential businesses beyond what they did including takeout, construction, weed and alcohol. The courts would have to go along with it despite the limits on the exercise of federal power over matters not affecting interstate commerce.
In other words, while theoretically an Aus/NZ might have been attempted by a President Hillary in an alternate universe, the end result was likely violence if not civil war both against the red staters and the BLMers.
And as for the shoulda, here's a good argument re New Zealand from GBD Bhattacharya
Jacinda Ardern was never the pandemic heroine she was made out to be.
www.spiked-online.com