President-elect Joe Biden will convene a coronavirus task force to examine the No. 1 problem confronting him when he takes office in January, while President Donald Trump pursues several long-shot gambits to hold on to his job.
Biden on Monday is to meet with an advisory board to examine how best to tame a pandemic that has killed more than 237,000 Americans.
"Dealing with the coronavirus pandemic is one of the most important battles our administration will face, and I will be informed by science and by experts," Biden said in a statement on Monday.
The group of scientists and experts will liaise with local and state officials on the pandemic response, including how to safely reopen schools and firms and tackle racial disparities.
Biden cleared the threshold of 270 Electoral College votes needed to win the White House on Saturday, four days after the November 3 election. He beat Trump by more than 4 million votes nationwide, making Trump the first president since 1992 to lose re-election.
But Trump has not acknowledged defeat and has launched an array of lawsuits to press claims of election fraud for which he has produced no evidence. State officials say they are not aware of any significant irregularities.
Trump plans to hold rallies to build support for his challenge to the election results, campaign spokesman Tim Murtaugh said.
Biden's advisers are moving ahead and considering candidates for top Cabinet posts. But the transition cannot shift into high gear until the US General Services Administration, which oversees federal property, certifies the winner.
Emily Murphy, the Trump appointee who runs the agency, has not yet done so and a GSA spokeswoman gave no timetable for the decision.
Until then, the GSA can continue providing Biden's team with offices, computers and background checks for security clearances, but they cannot yet enter federal agencies or access federal funds set aside for the transition.
The Biden campaign on Sunday pressed the agency to move ahead.
"America's national security and economic interests depend on the federal government signaling clearly and swiftly that the United States government will respect the will of the American people and engage in a smooth and peaceful transfer of power," the campaign said in a statement.
Trump, however, has shown no signs he will engage in a transition.
Murtaugh said Trump will hold a series of rallies to build support for the legal fights challenging the outcome.
Trump will seek to back up his as yet unsubstantiated accusations of voting fraud by highlighting obituaries of dead people the campaign said voted in the election, Murtaugh said.
Trump also announced teams to pursue recounts in several states. Experts said that effort, like his lawsuits, are unlikely to meet with success.
"The chances of a recount flipping tens of thousands of votes across multiple states in his favour are outside anything we have seen in American history," William Antholis, director of the University of Virginia's Miller Centre think tank, wrote in an essay on Sunday.
Leaders from across the globe have congratulated Biden, including some Trump allies, but many of Trump's fellow Republicans have yet to recognise the Democrat's victory.
Republican attorneys general from Louisiana, Kentucky, Missouri and Oklahoma said they will take legal action on Monday to help the Trump campaign challenge how Pennsylvania has handled mail ballots, a popular option this year for voters seeking to avoid coronavirus exposure at crowded polling locations.
Pennsylvania, the state that clinched Biden's victory on Saturday, has been one of the most hotly contested battlegrounds of the election.
Trump has repeatedly criticised mail voting as insecure, though he himself has voted that way in past elections and election experts say it is as reliable as other methods.