(AP) - Confronting twin health and economic crises, President Donald Trump announced Wednesday he will invoke emergency powers to marshal critical medical supplies against a coronavirus pandemic threatening to overwhelm hospitals and other treatment centers. The Senate acted on the economic front, approving legislation to guarantee sick leave to workers sickened by the disease.

Trump described himself as a “wartime president" as virus cases surged and the markets fell, and he took a series of extraordinary steps to steady a battered nation, its day-to-day life fundamentally altered.

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Most immediately, Trump said he would employ the Defense Production Act as needed, giving the government more power to steer production by private companies and try to overcome shortages in masks, ventilators and other supplies.

Trump also said he will expand the nation's testing capacity and deploy a Navy hospital ship to New York City, which is rapidly becoming an epicenter of the pandemic, and another such ship to the West Coast.

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The Housing and Urban Development Department will suspend foreclosures and evictions through April. A growing number of Americans face losing jobs and missing rent and mortgage payments.

But as Trump laid out efforts to steady the economy, the markets plummeted. Gone were the last of the gains that the Dow Jones Industrial Average had made since Trump took office.

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Administration announcements came on a fast-moving day of developments across the nation's capitol, its empty streets standing in contrast to the whirlwind of activity inside the grand spaces of the White House and the Capitol.

The Senate overwhelming passed a second coronavirus response bill, sending it to Trump to enact with his signature. The vote was a lopsided 90-8 despite worries by many Republicans about a temporary new employer mandate to provide sick leave to workers who get COVID-19. The measure is also aimed at making diagnostic tests for the virus free.

Meanwhile the administration pushed forward its broad economic rescue plan, which proposes $500 billion in checks to millions of Americans, with the first checks to come April 6 if Congress approves the plan. Trump and Canadian Prime Minister Justin Trudeau jointly announced that the U.S.-Canada border would be closed, except for essential personnel and for trade. The virus is afflicting people in both countries.

The White House urged hospitals to cancel all elective surgeries to reduce the risk of being overwhelmed by rising cases. The president was pressed on why a number of celebrities, like professional basketball players, seemed to have easier access to diagnostic tests than ordinary citizens.

“Perhaps that's the story of life," Trump said. "I've heard that happens on occasion.”

Trump dismissed talk from his own treasury secretary, Steven Mnuchin, who suggested that the nation could face 20% unemployment at least in the short term.

That's an "absolute total worst case scenario," Trump said. “We're no way near it."

The administration has told Americans to avoid groups of more than 10 people and the elderly to stay home while a pointed reminder was given to millennials to follow the guidelines and avoid social gatherings. Trump likened the effort to the measures taken during World War II and said it would require national “sacrifice."

“It's a war," he said. "I view it as a, in a sense, a wartime president. It's a very tough situation.”

No long able to run for reelection on a healthy economy, he was taking on the mantle of a wartime leader after played down the severity of the crisis for weeks.

The president also employed more nativist, us-vs-them rhetoric at the briefing, continuing his recent habit of referring to the coronavirus as the “Chinese virus,” which has been sharply criticized as racist. “It's not racist at all," Trump said. “It comes from China, that's all."

He was asked about a report that a White House aide had referred to the virus as the “Kung flu" when talking to an Asian-American reporter and Trump did not signal disapproval of the offensive term.

The Defense Production Act gives the president a broad set of authorities to shape the domestic industrial base so that it is capable of providing essential materials and goods needed in a national security crisis.

The law allows the president to require businesses and corporations to prioritize and accept contracts for required materials and services. It also allows the president to provide incentives for the domestic industrial base to expand the production and supply of critical materials and goods, according to a March 2 report by the Congressional Research Service.

Trump also said he would soon invoke a rarely used federal statute that would enable the U.S. to tighten controls along the southwest border because of the new coronavirus, based on a recommendation of the U.S. surgeon general.

The president said the law, intended to halt the spread of communicable diseases, would give authorities “great latitude" to help control the outbreak. Earlier, U.S. officials told The Associated Press that the administration would invoke the law to immediately turn back all people who cross the border illegally from Mexico and to refuse people the right to claim asylum there.

More than eight weeks after the first U.S. case of the virus was detected, the federal government is still struggling to conduct widescale testing for the virus. Compounding the problem, laboratories are reporting shortages of key supplies needed to run tests.

Vice President Mike Pence reiterated Wednesday that testing should give priority to those most likely to have COVID-19.

“It’s important to remember that people without symptoms should not get tested,” Pence said. “We want to make sure the supply of testing is there for those who need it most.”

Deborah Birx, who is coordinating the White House response, cautioned there has been a backlog of swabs waiting in labs to be tested, and as that backlog clears “we will see the number of people diagnosed dramatically increased” in the next few days.

Birx said the science discovering how long the virus can be transmissible on hard surfaces helped prompt the administration’s tightening of recommendations on social distancing. “None of us really understood the level of surface piece," she said. “We’re still working out how much is it by human-human transmission and how much is it by surface.” She said: "Don’t exposure yourself to surfaces outside the home.”

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

Birx also renewed her call for younger people to follow federal guideline and stop meeting in groups.

She said there have been “concerning reports” from France and Italy about young people becoming seriously ill. The task force last week urged young generations to avoid going out to bars and restaurants and to not meet in groups of more than 10 people.

“We cannot have these large gatherings that continue throughout the country for people who are off work,” Birx said. She added that the federal pandemic task force so far has not seen any “significant mortality” in children.

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