An interesting article in the NY Times makes the claim that much of the SARS-CoV-2 spread in the USA relates back to an outbreak in NYC in early March. This outbreak was primarily seeded from the European outbreak, not directly from China.
These assertions are based on genomic sequencing data of >5350 SARS-CoV-2 infections in North America on Nextstrain.org. and made by Nate Grubaugh, a Yale epidemiologist who is a member of the Nextstrain team. The key result is that there are two primary genomic strains -- one more related to the Wuhan strain that first struck Washington and the northwest and didn't spread too severely, and the other more related to the European (Italian) strain that seems to have had its first outbreak in NYC and spread around USA from there.
Travel from Europe to USA was restricted on 3/13 -- too bad it wasn't done two weeks earlier, and too bad travel from NYC was not restricted, and too bad NYC took so long to lock down. This may have prevented much of the pandemic spread throughout the USA. The article mentions that these steps would have likely stemmed the tidal wave of spread throughout the country.
But Monday morning quarterbacking and political blame games won't solve the current problem -- it has spread throughout out country, and we need to figure out what to do about it now. But this understanding does give us insights into how to better contain any future epidemic outbreaks.