WASHINGTON — President Donald Trump on Sunday called on Americans to cease hoarding groceries and other supplies, while one of the nation's most senior public health officials called on the nation to act with more urgency to safeguard their health as the coronavirus outbreak continued to spread across the United States. Dr. Anthony Fauci says he would like to see aggressive measures such as a 14-day national shutdown.

Trump assured Americans, after speaking with leading grocery chain executives, that grocers would remain open and that the supply chain remained healthy. Vice President Mike Pence urged Americans to only buy the groceries they need for the week ahead.

"You don't have to buy so much," Trump said at a news conference. "Take it easy. Just relax."

The comments from the president after the government's top infectious disease expert said he would like to see aggressive measures such as a 14-day national shutdown that would require Americans to hunker down even more to help slow the spread of the coronavirus.

Still, Dr. Anthony Fauci said travel restrictions within the United States, such as to and from hard-hit Washington state and California, probably will not be needed anytime soon.

The push by one of the nation's foremost public health experts for Americans to act with greater urgency came as officials in Washington began preparing for what is expected to be a long-haul effort to try to stem the virus that has upended life around the globe.

At the White House, Trump tuned in to the online church service at Gainesville's Free Chapel on what he designated as a national day of prayer and held a conference call with grocery and supply chain executives on how to keep food and other necessary supplies flowing to Americans. 

New protocols were on the way to protect the president and his staff. Starting Monday, those who enter the White House complex will have their temperatures taken, according to a person familiar with the matter who spoke on condition of anonymity to discuss protocols not yet announced. This would expand on screenings that began Saturday for those in close proximity to the president and vice president.

House Speaker Nancy Pelosi, D-Calif., said Congress had started work on a new aid package after the one just approved by the House early Saturday, which provided direct relief to Americans suffering physically, financially and emotionally from the coronavirus pandemic. It included sick pay and other resources and was pending in Senate.

"We have already begun work to develop a third emergency response package," Pelosi wrote in a letter to colleagues.

With the U.S. Capitol among the many iconic landmarks closed to tours, Pelosi also urged lawmakers to have most of their Washington staff telework from home, as health officials urge social distancing. House lawmakers are away on weeklong recess and many have already curtailed office visits at their local offices, as well.

Fauci, the public face of the administration's messaging during a round of morning TV interviews, said the country should do as much as "we possibly could," even if officials were criticized for overreacting. He said he raised the issue of measures such as a shutdown with the Trump administration, and said officials were open to his ideas.

"I think Americans should be prepared that they are going to have to hunker down significantly more than we as a country are doing," said Fauci, a member of the White House task force on combating the spread of coronavirus. He heads the National Institute of Allergy and Infectious Diseases at the National Institutes of Health.

Treasury Secretary Steven Mnuchin said he will ask Congress to reinstate powers that were used during the 2008 financial crisis to support the economy as the coronavirus threatens to significantly slow U.S. business activity in the weeks ahead.

Fauci said the elderly and those with underlying medical conditions should already be hunkering down, but other Americans, too, should consider further restricting their outside activity, including teleworking if possible, avoiding travel and skipping meals in restaurants.

"Everything is on the table," he said. "Right now, myself personally, I wouldn't go to a restaurant. I just wouldn't because I don't want to be in a crowded place. ... I don't want to be in a situation where I'm going to be all of a sudden self-isolating for 14 days." The virus has an incubation period of anywhere from two days to 14 days before symptoms emerge. 

For most people, the new coronavirus causes only mild or moderate symptoms, such as fever and cough. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia. The worldwide outbreak has sickened more than 156,000 people and left more than 5,800 dead. The death toll in the United States is more than 50, while infections neared 3,000 across 49 states and the District of Columbia. 

The vast majority of people recover. According to the World Health Organization, people with mild illness recover in about two weeks, while those with more severe illness may take three weeks to six weeks to recover.

Trump in recent days has imposed sweeping travel restrictions for much of Europe. On Saturday, he added the United Kingdom and Ireland to a list of countries that would face travel restrictions over the next 30 days. The State Department on Sunday said it would allow U.S. personnel to leave their diplomatic or consular posts worldwide if they or family members were medically determined to be at a higher risk of falling very ill if exposed to the virus.

Trump also has pledged broadened U.S. testing for the virus as major employers such as Apple Inc. have sent workers home to telework and several states and big cities, including Los Angeles and Boston, shuttered down schools for a week or more.

Positive tests hit close to Congress and the National Institutes of Health. 

On Sunday, Democratic Rep. Adam Schiff, chairman of the House Intelligence Committee, said a former staff member tested positive for COVID-19. That staffer, Daniel Goldman, the attorney who led Democratic questioning during the House impeachment hearings, had left the office 10 days ago and he's believed to have contracted the virus after his departure.

"We will still be taking additional precautions over the next few days," Schiff said. "The former staffer is feeling better and no current staff have reported any flu-like symptoms at this time."

NIH reported Sunday that one of its staff working in its division on arthritis and musculoskeletal and skin diseases had tested positive for COVID-19, its first case. NIH said the person was not involved in patient care and was now quarantined at home and "doing well."

Trump has suggested that restrictions on travel within the U.S. to areas hit hard by the coronavirus pandemic could be next. But Fauci on Sunday played down that or having major national lockdowns on the level now seen in European countries such as Italy and Spain.

"We feel that with rather stringent mitigation and containment, without necessarily complete lockdown, we would be able to prevent ourselves from getting to where, unfortunately, Italy is now," Fauci said.

"With regard to domestic travel bans, we always talk about it, consider everything. But I can tell you that has not been seriously considered, doing travel bans in the country. ... I don't see that right now or in the immediate future."

More than the crisis was on Trump's mind. He tweeted that he was considering a full pardon for Michael Flynn, his disgraced former national security adviser, and he directed barbs at a familiar target, Senate Democratic leader Chuck Schumer of New York.

White House economic adviser Larry Kudlow expressed confidence that supply lines such as food for stores will be largely unaffected by the virus outbreak. 

"I've read about some situations where this is a difficulty, but most of our supply lines are working pretty well in the domestic United States," he said. "I mean, there's a huge economic challenge here. Do not get me wrong, a huge economic challenge. On the other hand, most of America is still working. ... Factories are not shutting down across the country, at least not yet."

Trump said he tuned in to services being streamed from the Free Chapel, an evangelical Gainseville, Georgia, church that like many congregations around the country was holding services without churchgoers in the pews.

Fauci spoke on NBC's "Meet the Press," CNN's "State of the Union," ABC's "This Week," "Fox News Sunday," and CBS' "Face the Nation." Kudlow appeared on CBS.