THE UNITED STATES is approaching a grim milestone, recording nearly as many deaths in a single day from the coronavirus pandemic as the 2,977 people who died in the terrorist attacks of Sept. 11, 2001. Both the victims of terrorism and the virus were cut down, their lives ended prematurely and beyond their control. But the current threat is not beyond our control. The wave of infections now swamping the country will seed even more sickness and death unless we — the survivors — stand up and stop it.

Just as after 9/11, when the nation reoriented its priorities and faced the threat of terrorism, we must again, as a whole society, do what is right. Everyone. No more pockets of college students partying without masks, no more demonstrations threatening to “liberate” states, no more motorcycle rallies, summer camps, church choirs and weddings that ignore mitigation measures and become superspreading events. We may have been ignorant about the virus in March, but we know now: It spreads person to person, two-fifths of infected people can be asymptomatic, it is life-threatening for the elderly and people with comorbidities, it spreads faster in enclosed spaces, and the threat can be reduced when people wear masks to prevent inhaling the virus particles or expelling them to others.

It is true that errors were made in responding to the pandemic, not least by President Trump, who showed negligence and utter cluelessness when faced with a threat that has now killed some 274,000 Americans, and by the estimate of Robert Redfield, director of the Centers for Disease Control and Prevention, could reach close to 450,000 by February in what he called “the most difficult time in the public health history of this nation.”

The greatest mistake would be not to learn the lessons of this catastrophe. Mr. Trump has not. We still can.

We must not act as a collection of free spirits in denial, but rather as a cohesive nation that recognizes the enormity of the threat. Every single person in the United States should commit themselves to wearing a face mask in public, to rigorously follow the rules of distancing and good hygiene, to avoid tightly enclosed spaces and events that could recklessly transmit the virus. The vaccines are coming, but we can’t wait to adjust our behavior. Avoid bars, restaurants and other enclosed venues where the virus lurks, and avoid unnecessary travel. For those grocery stores, schools and other places that are essential, and must stay open, and for the courageous workers who run them, mitigation measures must be everybody’s business. No complaints.

Look at France. New restrictions went into effect on Oct. 30. On a seven-day rolling average, the number of daily new cases dropped from 79.5 per 100,000 people on Nov. 7 to just 15.9 on Dec. 1. The United States has gone from 10.4 on Sept. 12 to 48.9 on Dec. 1. France crushed the curve. We are still climbing it.

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