https://www.cnn.com/2020/07/16/politics/us-travel-bans-late-new-york-city-coronavirus/index.html

The US restricted travel from China on February 2 and from Europe on March 13, but by March 8, Covid-19 was already circulating among the community in New York City and, by March 15, community transmission of the virus was already widespread, the analysis found.
What was circulating most closely matched the strain of the virus circulating in Europe, not China, which President Donald Trump has repeatedly blamed for not preventing its spread to the US.
By the time the Trump administration had placed travel restrictions on Europe, the importation of the virus and the community spread of the disease had already started in New York City, according to the report. Testing was limited at the start of the epidemic in New York City, which allowed people with undetected cases to spread the virus.