From the Rose Garden, Trump said, "I am officially declaring a national emergency," unleashing as much as $50 billion for state and local governments to respond to the crisis.
Trump also announced a range of executive actions, including a new public-private partnership to expand coronavirus testing capabilities with drive-through locations, as Washington tries to subdue the virus whose spread is roiling markets, shuttering institutions and disrupting the lives of everyday Americans.
But he asserted "I don't take responsibility at all" for the slow rollout of testing.
The hard-fought aid package will provide free testing, sick pay for workers, enhanced unemployment benefits and bolstered food programs.
The House passed the bill after midnight on a bipartisan vote, 363-40. It now goes to the Senate..
"We did what we said we were going to do: Put families first," said House Speaker Nancy Pelosi.
Trump tweeted his approval, all but ensuring that wary Republicans would join with a robust vote. "Good teamwork between Republicans & Democrats as the House passes the big CoronaVirus Relief Bill," he tweeted Saturday. "People really pulled together. Nice to see!"
I fully support H.R. 6201: Families First CoronaVirus Response Act, which will be voted on in the House this evening. This Bill will follow my direction for free CoronaVirus tests, and paid sick leave for our impacted American workers. I have directed....— Donald J. Trump (@realDonaldTrump) March 14, 2020
Trump's tweet of approval instilled fresh energy in the measure, all but ensuring that wary Republicans would join with a robust vote.
The crush of activity capped a tumultuous week in Washington as the fast-moving virus left ordinary Americans suddenly navigating self-quarantines, school closures and a changed way of life.
The White House was dealing with the crisis on multiple fronts as it became increasingly personal to the president.
Trump has been known to flout public health advice - and was eagerly shaking hands during an event Friday - but acknowledged he "most likely" will be tested soon. This, after he was exposed to several people who have tested positive for the virus. The White House physician indicated later that Trump's interactions were low-risk and testing is not necessary.
Trump took a number of other actions to bolster energy markets, ease the financial burden for Americans with student loans and give medical professionals additional flexibility in treating patients during the public health crisis.
Central to the aid package from Congress, which builds on an emergency $8.3 billion measure approved earlier, are the free testing, sick pay and family leave provisions.
Providing sick pay for workers is a crucial element of federal efforts to stop the rapid spread of the infection. Officials warn that the nation's healthcare system could quickly become overwhelmed with gravely sick patients, as suddenly happened in Italy, one of the countries hardest hit by the virus.
The ability to ensure paychecks will keep flowing - for people self-quarantining or caring for others - can help assure Americans they will not fall into financial hardship. The legislation also offers three months of paid family and medical leave. Small and mid-sized employers will be reimbursed through tax credits.
Pelosi negotiated the deal with Treasury Secretary Steven Mnuchin in days of around-the-clock negotiations with cross-town phone calls, even as Trump was speaking at the White House.
Voting in the Senate is not yet set, with senators out of town for the weekend. But Senate Leader Mitch McConnell canceled a planned recess week and senators were scheduled to return Monday. He said he expects most senators will want to "act swiftly."
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Both Mnuchin and Pelosi promised a third coronavirus package will follow soon, with more aggressive steps to boost the U.S. economy, which economists fear has already slipped into recession.
The financial markets closed on an upswing after one of the worst nosedives since 1987.
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. 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 be over it.
Trump on Friday also told people to expect the imminent rollout of a web site "facilitated" by Google that would guide users through a series of questions to determine whether they should be screened for the virus. If testing is recommended, users would be directed to a local testing location, which could include parking lots at Walmart, Target, Walgreens and other chains.
"It's going to be very quickly done, unlike websites of the past," Trump said in a thinly veiled dig at the Obama administration's disastrous rollout in 2013 of its online health care marketplace.
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But how quickly is in question. Google said the website, from its life science division Verily, is still "in the early stages of development." Verily first plans to roll out testing out in the Bay Area of San Francisco, with the hope of expanding more broadly over time, the company said in a statement.
Trump said he was gratified that Brazilian President Jair Bolsonaro tested negative for the virus, after the pair sat next to each other for an extended time last weekend at Trump's Mar-a-Lago club. A senior aide to Bolsonaro tested positive.
The White House physician, Sean Conley, said in a memo late Friday that Trump was also exposed to a second guest at the club dinner, "sharing the table with the president." That guest has since tested positive for the virus. Still, Conley said he regarded the interactions as low risk and testing "is not currently indicated."
Trump's daughter, Ivanka Trump, worked from home Friday after meeting Australian Home Affairs Minister Peter Dutton, now in isolation at a hospital after testing positive for the coronavirus.
Attorney General William Barr, who also met the Australian official, stayed home Friday, though he "felt great and wasn't showing any symptoms," according to his spokeswoman, Kerri Kupec.