The virus was circulating in the United States undetected, by January. As one of the largest, most heavily traveled countries in the world, there was little hope that they would be able to shut their borders early enough to stave off any infections.
How would temperature and subjective screening prevent these asymptomatic patients from infecting many others?
Doing widespread spot testing across the country would've identified the communities where the virus was extant. From there we would've known where to focus the brunt of universal testing, tracking and quarantining.
Just the fact that we are still fiddling with estimates of what percentage of CV infected people are asymptomatic is a travesty. We should have long ago conducted enough statistical sampling to have a very clear picture what was happening in our communities.