(CNN) America's top infectious diseases expert is warning that hundreds of thousands of Americans could die unless every citizen joins an effort to blunt the coronavirus pandemic -- only to be contradicted by President Donald Trump , who insists the virus is under "tremendous" control .

The fresh sign of Trump's unwillingness to accept the full, sobering reality of the outbreak came as an anxious America knuckles down to its new self-isolating reality. The country is bracing for the full fury of the virus that is already escalating sharply and is set to subject the foundations of basic life — the nation's health care, economic and political systems — to a fateful test.

Amid calls for a stronger federal response, Trump urged the nation's governors late Monday morning to try to secure additional medical equipment on their own without waiting for the federal government to intervene, though he did say they would try to help.

"We will be backing you, but try getting it yourselves," Trump said on the call, a person familiar with the call told CNN's Kaitlan Collins. He was discussing what health experts say is a serious need for more respirators and ventilators to deal with the influx of coronavirus patients.

Meanwhile, the number of US infections raced up to at least 3,900, including 70 deaths, up more than 500 cases in a day and up from a caseload of 457 a week ago, showing how the crisis, which may not reach its peak for weeks, is accelerating.

Among his tweets on coronavirus Sunday, Trump suggested that his entire focus was not on the national emergency: He tweeted that he was thinking about a full pardon for his former national security adviser Michael Flynn, who admitted lying to the FBI.

Earlier that day, Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, warned that the US could face a similar crisis as Italy if citizens do not fully embrace self-isolation and social distancing, which are designed to flatten the curve of infections.

Asked whether hundreds of thousands of Americans could die, Fauci said on CNN's "State of the Union" : "It could happen, and it could be worse." Fauci added that the limits on public life were designed to "try and make that not happen."

"If we go about our daily lives and not worry about everything," the death toll could be high, Fauci said. "People sometimes think that I'm overreacting. I like it when people are thinking I'm overreacting because that means we're doing it just right." Fauci also said he had not ruled out calling for a national lockdown in order to stem the spread of the virus.

The administration is expected to release new guidelines on social distancing -- for instance relating to bars and restaurants -- on Monday. The Centers for Disease Control and Prevention on Sunday recommended not holding gatherings of 50 people or more for the next eight weeks. The White House Correspondents Association, which is urging its members to work from home when possible, has instituted a seating arrangement in which every other chair in the briefing room is vacant, and there are mandatory temperature checks for anyone seeking to enter White House grounds.

But serious questions remain over whether Trump's administration -- which was slow to recognize the threat , mischaracterized its impact and seemed most concerned about mitigating political damage -- has now got the federal act together.

Trump flagrantly contradicted Fauci's warnings at a White House briefing Sunday at which he celebrated the Federal Reserve's decision to cut interest rates to 0% to help the shocked economy.

"It's a very contagious virus, it's incredible, but it's something we have tremendous control of," the President said.

In a possible indication of how Trump's repeated misinformation is having an impact, a new poll by NBC and the Wall Street Journal Sunday showed that while seven in 10 Democrats are worried that they or someone in their family may catch the coronavirus, only 40% of Republicans, who are more likely to believe what they hear from the President and in conservative media, feel the same.

Trump's upbeat predictions about the coronavirus crisis did not just contrast with Fauci's warnings, they also clashed with the conditions being experienced by local officials.

"We have been behind on this disease since day one," New York Gov. Andrew Cuomo, a Democrat, told Wolf Blitzer on "The Situation Room."

"I believe on any projection that that flattening of the curve is not going to be enough. I don't see it as a curve. I see it as a wave. And the wave is going to crash on to our hospital system."

The coronavirus also dominated the opening exchanges of the CNN Democratic presidential debate on Sunday evening -- with former Vice President Joe Biden and Vermont Sen. Bernie Sanders standing six feet apart in a Washington studio to comply with government health guidelines -- both arguing they would be far better at handling the pandemic than Trump.

"This is like a war, and in a war you do whatever is needed to be done to take care of your people," Biden said.

Sanders was scathing about Trump's handling of the crisis.

"First thing we have got to do, whether or not I'm president, is to shut this President up right now, because he's undermining the doctors and the scientists who are trying to help the American people," Sanders said. "It is unacceptable for him to be blabbering with un-factual information, which is confusing the general public."

Progress on testing logjam

One of the big criticisms of the administration's effort has been that it failed to make millions of coronavirus testing kits available sufficiently quickly.

Vice President Mike Pence announced Sunday that as of this week, more than 2,000 labs would come online nationwide with high-speed testing facilities.

He said that the new system would allow all Americans who need to be tested to go to a community site outside their normal health networks for testing. Officials asked that those at highest risk, the elderly and patients with pre-existing conditions be given priority.

Top officials were still unable to give full figures Sunday on how many Americans have now been tested after the disastrously slow roll out of diagnosis kits. The lack of clarity is seriously hampering efforts to keep pace with the disease.

Ohio Gov. Mike DeWine suggested on CNN's "State of the Union" that an estimated 100,000 undiagnosed infections could already have happened in his state alone.

"We have got a lot of people walking around in Ohio who are positive who've not been tested. Some don't know it. Some may never know it," the Republican governor said.

Despite his calls for national unity, Trump exploded at the media on Sunday after it emerged that his announcement that Google would quickly open a national virus testing website was at best premature and at worst highly misleading.

"The Fake and Corrupt News never called Google. They said this was not true. Even in times such as these, they are not truthful. Watch for their apology, it won't happen. More importantly, thank you to Google!" Trump tweeted.

The President, as is his custom, managed to make the story of coronavirus all about him this weekend. A White House reversal led him to get tested for the disease after interacting with several people last weekend who have since been diagnosed with COVID-19. Happily, the President, who shook hands with top CEOs at a press conference on Friday in contravention of his own government's advice, tested negative for the novel coronavirus, according to the White House.

While Trump's response has been marked by chaos and confusion -- The Washington Post on Sunday reported internal power games raging in the White House over the virus -- true leaders have been emerging all over the country. Governors, mayors and local officials have been making timely, high-stakes decisions and providing accurate information that sometimes surpasses that dispensed in White House briefings, which remain filled with self-congratulation and fawning praise for the President.

House Speaker Nancy Pelosi and Treasury Secretary Steven Mnuchin solved one of the big questions of the Trump era: will the bitter recriminations between the White House and Congress -- especially in the wake of the impeachment drama -- stop both sides working together in a time of national crisis?

Mnuchin and Pelosi swapped multiple calls late last week brokering an economic stimulus plan that includes money for sick workers and small businesses hurt by the crisis. The Senate is expected to act on the package this week. The Speaker also said an additional plan for economic mitigation was already on the way

And the White House is likely to ask Congress this week for another round of funding specifically for the Pentagon, Department of Homeland Security and Department of Veterans Affairs, two White House officials told CNN. Administration officials have discussed relying on the VA to supplement the broader health care system by taking care of civilians in the event the coronavirus crisis worsens.

New problems emerged with the federal authorities' response to the crisis over the weekend, which caused fresh tension with local political leaders.

Meanwhile, the massive lines at airports -- with passengers returning from abroad huddled in unhealthy crowds for virus screening -- suggest the government was unprepared for Trump's sudden orders.

"I want to make known my strong concerns and disappointments with the federal government's lack of preparedness in issuing new directives regarding airport screening," Chicago Mayor Lori Lightfoot said.

Illinois Gov. J.B. Pritzker said on NBC's "Meet the Press" that a White House staffer called to yell at him after he complained about the long lines at O'Hare airport.

"They should have increased the Customs and Border Patrol numbers. And they should have increased the number of CDC personnel on the ground doing those checks. They did neither of those," the Democratic governor said.

Trump asks Americans not to besiege supermarkets

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Hospitals and medical staff are awaiting a spike in patients unsure whether they have sufficient breathing machines and intensive care beds for a rush of gravely ill patients.

Fauci said that in the worst case scenario he wants to prevent there may not be sufficient ventilators available for patients who need them.

"That's when you're going to have to make some very tough decisions," he told CNN's Brianna Keilar.

Fauci's sobering comments came as the fabric of everyday American life ebbed in the biggest economic and societal shutdown of the modern age.

DeWine suggested schools in his state could be out for the rest of the academic year. Michigan Gov. Gretchen Whitmer signed an order outlawing price gouging of items like cleansing and disinfecting supplies that are in high demand.

City authorities in Washington, D.C., introduced new restrictions meant to cut down on the numbers of people in bars and restaurants after large crowds were out celebrating St. Patrick's Day over the weekend.

A trade group representing food and retail companies like Clorox, Procter & Gamble and PepsiCo told the State Department and the US Trade Representative they fear other countries cutting off exports to the US , which could exacerbate the public health emergency.

The group is particularly concerned about countries restricting chemicals, ingredients and products they manufacture from getting to the US.

Trump held a call with grocery, food and beverage corporate leaders on Sunday about supply chain concerns.

He urged Americans to stop besieging stores after a weekend in which basic staples like pasta, meat, toilet paper rolls and cleaning products vanished from supermarket shelves.

This story has been updated to include additional reporting.