Deborah Birx, the White House's coronavirus response coordinator, told NBC's "Today" Monday that a projection of 100,000–200,000 U.S. coronavirus deaths is based on the presumption that citizens follow social-distancing guidelines "almost perfectly."

Why it matters: Birx said she is unsure that people are following the guidelines and cited images circulating online of people around the world congregating in large groups.

What she's saying: "Cities that don't social distance, that don't stay at home, that believe you can have social interactions, that believe you can have gatherings at home of 20 and 10 people even — that is going to spread the virus, even if everyone looks well," Birx said.

The big picture: The U.S. has reported more than 143,000 cases and 2,500 fatalities from the coronavirus as of Monday morning, according to data from Johns Hopkins University.

Go deeper: Fauci says Trump backed off Easter reopening after seeing coronavirus projections