At a White House ceremony to honor veterans, President Donald Trump told the assembled guests, “I’m not supposed to shake his hand” — and then did just that with the father of a fallen Marine.

The exchange seemed harmless enough at the time, despite violating social-distancing guidelines. But it, and the many other interactions people have had with the president since, have taken on a more worrisome tone in the wake of the president’s Covid-19 diagnosis just four days later.

All told, hundreds of people — some masked, many not — came into contact with Trump in the week leading up to his positive COVID test, according to interviews with witnesses and a review of White House schedules, news accounts, and photographs.

Most famously, the Rose Garden event to announce Amy Coney Barrett as a Supreme Court nominee attracted 150 people, at least eight of whom have since tested positive for the illness. Between it and Friday, when Trump was helicoptered to Walter Reed National Military Medical Center, he headlined a string of risky events — many indoors —  that have sent people scrambling to get tested.