What Trump doesn’t mention, however, is his administration’s failure to restrict travelers from Europe until it was too late. An investigation by The Intercept shows that travel from Europe was a key facilitator of the virus’s spread in the U.S. — a large amount of the first Covid-19 cases in the U.S. can be traced to Europe. While the China restrictions operated as an attempt to close the front door to infections from the nation where the pandemic started, the back door — travel from Europe, where the virus took hold particularly fiercely in Italy — remained wide open until the middle of March and can be connected to a surge of cases in the U.S., especially in the New York area.

When pressed about his delayed response to the coronavirus pandemic, President Donald Trump has repeatedly cited the U.S. travel restrictions imposed on China, which went into effect on February 1. “Something we did very well is when we stopped the inflow from China at a very early level,” Trump said on March 29. “That was a good thing to do, a great thing to do.”

The Intercept reviewed hundreds of media reports detailing the first recorded coronavirus cases — known as the “index cases” — in U.S. states and territories. European travel preceded the index cases in at least 13 states and territories, compared to only six from China. There were as many imported index cases from cruise ships (six) as from China, while Italy accounted for at least 10 of the first Covid-19 cases.

For instance, Missouri’s first case was a young woman who studied abroad in Italy, while a high school trip to Milan was behind Rhode Island’s index case. Travelers from Italy brought it to Florida, Georgia, Oklahoma, Colorado, New Hampshire, and South Carolina. Italian tourists brought Covid-19 to Puerto Rico, and a Navy reservist stationed in Italy brought it to Maine.

A review of the known index cases also shows that the coronavirus often spread from the northeastern United States, indicating a chain of transmission from China to Europe to the East Coast of the U.S., and from there to other U.S. states. Many state governments have declined to publicly share data on the provenance of their early cases, but some, like New Mexico, Kansas, North Dakota, and Idaho, confirmed that their first cases had links to New York or the northeastern U.S.

Index Cases in the United States

Total China 5 Cruise ships 6 Italy 10 Other Europe 3 Total Europe 13

From February 1 to when flight restrictions went into effect on the Schengen zone (the 26 European states without internal border checks) and Britain and Ireland, on March 14 and March 17 respectively, more than 10,000 direct flights from Europe had arrived in 12 major American airports, according to data from tracking agency FlightAware. Though this number includes some cargo flights, their proportion to passenger flights is very low. Occupancy data from Air France/KLM shows that those flights might have carried an estimated 1,000,000 people into the country.

In the six weeks prior to the European travel bans, the U.S. was exposed to a massive amount of travelers from a highly infected region. During that time, there were almost no checks in international airports for passengers coming from Europe, as American authorities focused their screening efforts on China travelers. The China travel restrictions were mostly cosmetic anyway — the Chinese government banned flights from the Hubei region on January 23 and was sharply reducing its cases through harsh lockdowns and quarantines.

The Trump administration appears to have considered — and rejected — an early European travel ban in January. The Washington Post reported that Matthew Pottinger, the deputy national security adviser, had proposed a travel ban on affected European countries in late January, which was supported by health officials but was rebuffed by Trump and Treasury Secretary Steven Mnuchin. As Trump faces increased criticism for a period of calamitous early inaction, he has sought to focus the blame on China, and on Saturday he published a tweet trying to discredit a New York Times story on the role of European travel in New York’s epidemic.

The impact from Europe was particularly acute on the East Coast of the U.S., where many of those flights landed. From February 5 to the implementation of the travel bans on March 14 and March 17, nearly 4,000 direct flights from Europe arrived at New York’s John F. Kennedy Airport and Newark Liberty International in New Jersey, far more than any other metropolitan area in the country. San Francisco, by contrast, where the caseload has been kept relatively low, had a little over 600 flights from Europe in that same time period. While San Francisco also took stricter preventative measures earlier on, like issuing its stay-at-home order five days before New York did, it was also subject to less exposure overall.

Six weeks of coronavirus exposure from Europe

Destination airport Date Original departure Numbers of flights JFK Airport 2/5 to 3/13 Schengen 1,569 2/5 to 3/16 U.K. and Ireland 1,189 Total 2,758 O’Hare International Airport 2/5 to 3/13 Schengen 585 2/5 to 3/16 U.K. and Ireland 188 Total 773 San Francisco International Airport 2/5 to 3/13 Schengen 351 2/5 to 3/16 U.K. and Ireland 278 Total 629 Los Angeles International Airport 2/5 to 3/13 Schengen 264 2/5 to 3/16 U.K. and Ireland 419 Total 683 Seattle-Tacoma International Airport 2/5 to 3/13 Schengen 147 2/5 to 3/16 U.K. and Ireland 114 Total 261 Hartsfield-Jackson Atlanta International Airport 2/5 to 3/13 Schengen 563 2/5 to 3/16 U.K. and Ireland 183 Total 746 Newark Liberty International Airport 2/5 to 3/13 Schengen 861 2/5 to 3/16 U.K. and Ireland 448 Total 1,200 Washington Dulles International Airport 2/5 to 3/13 Schengen 525 2/5 to 3/16 U.K. and Ireland 310 Total 809 Boston Logan International Airport 2/5 to 3/13 Schengen 305 2/5 to 3/16 U.K. and Ireland 401 Total 706 Dallas/Fort Worth International Airport 2/5 to 3/13 Schengen 104 2/5 to 3/16 U.K. and Ireland 171 Total 275 Detroit Metropolitan Wayne County Airport 2/5 to 3/13 Schengen 247 2/5 to 3/16 U.K. and Ireland 39 Total 286 Miami International Airport 2/5 to 3/13 Schengen 661 2/5 to 3/16 U.K. and Ireland 276 Total 916 Total flights from Schengen and U.K. to USA 10,042

A new study by researchers at NYU Grossman School of Medicine shows that, out of 91 patients studied, the vast majority of New York City’s coronavirus strains were identical to ones found in Europe. This provides additional evidence that Europe was the main source of Covid-19 in what became the pandemic’s global epicenter.

“We found that multiple chains of transmission were coming about two thirds from Europe, and the other third some from Asia and some from within other states of the United States,” said Dr. Adriana Heguy, director of the Genome Technology Center at NYU Langone and leader of the sequencing team. The proportion of strains from China was low, while there were many different European countries present. “You name the European country and it basically shows up: France, Austria, Netherlands, Italy, Madrid, I believe we had one. It was from everywhere in Europe,” she said.

Dr. Heguy said that the volume of flights from Europe is “probably the most likely explanation” for why New York City became the pandemic’s epicenter, adding that the virus might have been spreading in the U.S. from late January. “It’s very possible that there was already community transmission going on six to eight weeks” before recorded index cases, she said.