WASHINGTON — The sun had barely risen Monday when U.S. Surgeon General Jerome Adams took to the airwaves. “I want America to understand: This week, it’s going to get bad,” he said on NBC’s “Today.”

It got bad quickly.

For the first time since the coronavirus pandemic reached U.S. soil, the country reported more than 100 deaths in a single day, pushing the death toll past 500 and the infection total to more than 41,000.

As the number of confirmed cases of covid-19, the disease caused by the novel coronavirus, exploded across the country and the world, lawmakers on Capitol Hill spent much of the day locked in a bitter stalemate, unable to finalize the outlines of a $2 trillion stimulus package.

The Federal Reserve again announced an unprecedented set of actions meant to boost the faltering U.S. economy, but stocks on Wall Street tumbled again anyway. Leaders in Indiana, Maryland, Michigan, Virginia and a growing list of other states issued their strictest orders yet for Americans to help slow the spread of the coronavirus.

More than 100 million Americans — nearly 1 in 3 — are under orders from their governors to stay at home. Florida Gov. Ron DeSantis, a Republican, ordered all passengers on all flights that originate in New York or New Jersey to self-quarantine for 14 days when they arrive in the state. Rhode Island Gov. Gina Raimondo, a Democrat, ordered a similar quarantine for any person flying into her state.

But even as more states — and even other countries — continued to tighten restrictions in an effort to prevent hospitals and medical workers from being overwhelmed by the rapidly spreading virus, President Donald Trump signaled a wariness with the mounting economic consequences of bringing the nation to a halt.

"Our country wasn't built to be shut down," Trump said at a White House briefing late Monday afternoon. "At some point, we're going to be opening up our country. It's going to be pretty soon."

The president argued that a severe economic downturn could eventually pose a greater threat, in terms of the number of lives ruined, than the pandemic itself.

"If it were up to the doctors, they might say, 'Let's shut down the entire world,' " Trump said, making clear that he has little appetite for ongoing restrictions that threaten to further cripple the economy, even as experts have argued that they are critical to slowing the spread of the coronavirus.

Trump noted that tens of thousands of Americans die each year of the flu, and that thousands more perish each year in automobile crashes. "That doesn't mean we're going to tell everybody no more driving of cars," he said.

Asked about his desire to quickly get the nation moving again as health experts say the worst of the outbreak lies ahead for much of the country, Trump said the country can juggle health concerns while not shutting down completely.

"We can do two things at one time," he said, adding, "We can't have the cure be worse than the problem."

Vice President Mike Pence said the federal government will reexamine its social-distancing recommendations for Americans at the end of March. "We thought it was important for every American to take action, as tens of millions are, to help us slow the spread," Pence told reporters. "But at the end of this 15 days, we're going to get with our health experts, we're going to evaluate ways in which we might be able to adjust that guidance for the American people."

The initial 15-day period in which the administration urged people to work from home and avoid gatherings ends March 30.

Against Monday's backdrop of partisan gridlock, conflicting messages from the nation's leaders and growing financial turmoil, a deep and worsening public health crisis continued to engulf the nation.

The virus has claimed lives in at least 34 states, the District of Columbia and Puerto Rico, according to tracking by The Washington Post. By Monday afternoon, three dozen states had reported new deaths. New York, now a hotbed of the outbreak, reported the most, with 43. The state announced that its number of new cases had surged by more than 5,000 overnight to 20,875, in part because of expanded testing.

In the New York metropolitan area, 1 in 1,000 people has been infected by the disease — five times the rate in other parts of the country, said Deborah Birx, the head of the administration's coronavirus task force, said at the Monday briefing. Of those tested for the virus in the New York region, 28% were positive compared with 8% elsewhere in the country, she said. "All of my friends and colleagues [in New York], this is the group that absolutely has to self-isolate at this time," Birx said.

Officials have warned that the nation is likely to see a surge in new covid-19 cases this week, particularly in places where testing capacity has ramped up. The outbreak's acceleration has led an increasing number of governors to clamp down on movement in their states in a bid to slow the flood of infections.

Indiana, Michigan, Oregon and West Virginia became some of the latest states to announce stay-at-home orders on Monday. Wisconsin's governor said he plans to follow suit on Tuesday. The governors of Maryland and Massachusetts have ordered nonessential businesses to close, and Virginia Gov. Ralph Northam, a Democrat, said schools would remain closed for the rest of the academic year.

"The next two weeks are critical if we are to slow the spread of covid-19, and we must slow the spread," Indiana Gov. Eric Holcomb, a Republican, said in announcing a statewide stay-at-home order through April 6. "You must be part of the solution, not the problem."

Such actions mean tens of millions of Americans are now under directives to hunker down at home, leaving for only the most essential activities.

Other countries also ratcheted up efforts to slow the pandemic.

British Prime Minister Boris Johnson on Monday ordered far-reaching measures across the United Kingdom, including closing shops, libraries and places of worship and allowing people out only to buy essential items.

"Without a huge national effort to halt the growth of this virus, there will be a moment when no health service in the world could possibly cope," Johnson said in a national address.

India's largest cities began shutting down all but essential services and closed nearly all public transportation until the end of the month in a dramatic bid to check rising coronavirus infections. The government announced the suspension of all domestic flights, a move that alongside the cancellation of all passenger trains will bring the country to a virtual halt. Last week, all international flights were barred from landing in the country until March 29.

In New Zealand, Prime Minister Jacinda Ardern prepared the nation for a month-long lockdown, saying, "The worst-case scenario is simply intolerable." In Senegal, the military was set to begin enforcing a strict curfew as coronavirus cases mount in the West African country.

Meanwhile, even as he has backed social distancing in recent days, Trump has been eager to balance the public health implications of the pandemic with the dire impact that containment measures are having on the economy — including mounting job losses and a plummeting stock market.

Democratic New York Gov. Andrew Cuomo, no political ally of Trump, acknowledged Monday that the shutdown is unsustainable, and that the state needs to begin planning how to restart its economy. But he also said he has "no second thoughts" about pausing most of his state's commerce.

"I take total responsibility for shutting off the economy in terms of essential workers," Cuomo said during a news conference. "But we also have to start to plan the pivot back to economic functionality, right? You can't stop the economy forever."

New York Mayor Bill de Blasio, a Democrat, also acknowledged the economic implications of the current strategy. But during an appearance on CNN, he said that if left unchecked, the virus could cripple the health-care system.

"I understand people who say, 'Wow, this is an extraordinary sacrifice,' " de Blasio said. "It is, but if you don't slow this thing down, you'll sacrifice a lot more on the other end of the equation, and we've got to think about the human cost here."

In Washington, the Federal Reserve made its latest attempt to head off financial collapse, launching a massive effort Monday to keep money flowing to businesses, homeowners and local governments. The central bank said it would purchase an unlimited amount of U.S. Treasurys and mortgage-backed securities in an extraordinary effort to inject money into the economy and get investors off the sidelines.

By day’s end the stock market had continued to slide despite the government’s action, with the Dow Jones industrial average and the Standard & Poor’s 500 skidding about 3%.

As the number of infections and deaths climbed higher Monday, health workers continued to plead for more protective masks, gloves, testing swabs and other supplies. Officials in multiple states scrambled to open additional hospital beds for the expected influx of covid-19 patients.

Defense Secretary Mark Esper said he expects to deploy two Army field hospitals to New York City and Seattle this week to help combat the pandemic, although he said FEMA would make the final call on which cities would receive them.

Speaking at a Pentagon news conference Monday, Esper said "prepare to deploy orders" had been issued to five expeditionary medical units, including the Army field hospitals, which he said he expected to provide 248 beds each.

The defense secretary said he expects the pop-up hospitals to provide excess capacity for hard-hit areas as local authorities identify buildings that can be converted into temporary hospitals.

The Washington Post’s John Wagner, Felicia Sonmez, Derek Hawkins, Heather Long, Danielle Paquette, Jennifer Hassan, Lateshia Beachum, Brittany Shammas and Paul Sonne, Niha Masih and Joanna Slater contributed to this report.