The president acknowledged that the crisis — which has already killed thousands around the world and set off a plunge of world markets — could last until July or August and even plunge the nation into a recession. No country, including the United States, has it under control, he said, though he also suggested America could limit its death toll “if we do a really good job” responding now.

“Each and every one of us has a critical role to play in stopping the spread and transmission of the virus,” Trump said. “If everyone makes this change or these critical changes and sacrifices now, we will rally together as one nation, and we will defeat the virus, and we’re going to have a big celebration altogether. With several weeks of focused action, we can turn the corner and turn it quickly.”

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said that while some people may perceive the guidelines as inconvenient or going too far, they reflect a deteriorating assessment of the containment efforts and should be taken seriously.

“When you’re dealing with an emerging infectious diseases outbreak, you are always behind where you think you are if you think that today reflects where you really are. That’s not word speak. It means if you think you’re here,” Fauci said, gesturing to illustrate his point, “you’re really here because you’re only getting the results. Therefore, it will always seem that the best way to address it would be to be doing something that looks like it might be an overreaction. It isn’t an overreaction.”

The White House gave the country a 15-day window to flatten the soaring curve of infection, but some disease modelers see a trajectory that could create a crisis, similar to Italy, that would start to overwhelm the U.S. health care system in about 10 days.

Fauci called the 15 days “a trial” period for the guidelines to be reconsidered. “It isn’t that these guidelines are now gonna be in effect until July,” he clarified. “What the president was saying is the trajectory of the outbreak may go until then.”

The new guidelines come on the heels of Centers for Disease Control and Prevention guidance Sunday night that recommended the cancellation and postponement of gatherings of 50 people or more for the next eight weeks. It also comes after the Office of Personnel Management declared federal offices in the Washington, D.C., area open but with maximum flexibility for telework.

The president’s remarks reflect the increased urgency of the moment. As recently as Sunday, Trump was telling Americans to “relax” and that the pandemic would pass. And on Monday, White House economic adviser Larry Kudlow predicted that the outbreak would only impact the economy in the short term — “weeks and months,” he said, not years.

But hours later, Trump said the situation was “bad,” and administration officials pointed to new predictive modeling showing a need for more stringent social distancing measures. The case for aggressive social distancing is clear: A coronavirus vaccine is at least a year away, and the acceleration of the outbreak within the U.S. has put the it on track with some of the world’s hardest-hit nations.

“If everybody does what we’ve asked for in the next 15 days, we will see a dramatic difference,” said Deborah Birx, the White House’s coronavirus response coordinator.

More than a month-and-a-half into the response effort and after failed bids to prevent and then contain the disease’s spread, the Trump administration is now scrambling to put its full weight behind a messaging campaign aimed at convincing people to do something simple yet unnatural: stay home.

Still, public health experts said the administration has much work to do to sell Americans on such an abrupt change in habits and rebuild its credibility after weeks of mixed messages.

