Joe Biden, the US president-elect, took the first steps on Sunday towards moving into the White House in 73 days, as President Donald Trump again refused to admit defeat and tried to sow doubt about the election results.
With congratulations pouring in from world leaders and supporters nursing hangovers after a night of celebrations, Mr Biden and Kamala Harris, the vice president-elect, launched a transition website, BuildBackBetter.com, and a Twitter feed, @Transition46.
Meanwhile, Mr Trump played golf at his course near Washington, the same place where he was on Saturday when the US television networks delivered the news that Mr Biden had secured enough electoral college votes for victory.
"Since when does the Lamestream Media call who our next president will be?" Mr Trump complained in a tweet on Sunday.
Mr Trump plans to file a string of lawsuits in the coming week, according to his lawyer Rudy Giuliani, who said he had "a lot of evidence" of fraud.
But former president George W Bush said the "outcome is clear" and added that he had called "President-elect" Mr Biden and Ms Harris to extend his congratulations.
Mr Bush said "the American people can have confidence that this election was fundamentally fair... We must come together for the sake of our families and neighbours, and for our nation and its future."
Mr Biden's transition website lists four priorities: Covid-19, economic recovery, racial equity and climate change.
"The team being assembled will meet these challenges on day one," it said in a reference to January 20, 2021, when Mr Biden will be sworn in as the 46th President of the US.
Mr Biden, who turns 78 on November 20, is the oldest person yet to win the White House. Ms Harris, 56, a senator from California, is the first woman, first black person and first South Asian person to be elected vice president.
Mr Biden plans to unveil a task force on Monday to tackle the coronavirus pandemic, which has killed more than 237,000 people in the United States and is surging across the country.
He has also announced plans to rejoin the Paris climate accord and will reportedly issue an executive order on his first day in office reversing Mr Trump's travel ban on mostly Muslim countries.
Mr Biden has vowed to name a cabinet that reflects the diversity of the country, although he may have trouble gaining approval for more progressive appointees if Republicans retain control of the Senate – an outcome that will depend on two run-off races in Georgia in January.
The Trump campaign has mounted legal challenges to the results in several states, but no evidence has emerged of any widespread irregularities that would affect the results.
Mr Giuliani told the Fox News show Sunday Morning Futures that Mr Trump's team would file a lawsuit in Pennsylvania on Monday against officials "for violating civil rights, for conducting an unfair election [and] for violating the law of the state".
"The first lawsuit will be Pennsylvania. The second will either be Michigan or Georgia. And over the course of the week, we should get it all pulled together," Mr Giuliani said.
First Lady Melania Trump also chipped in, tweeting on Sunday: "The American people deserve fair elections. Every legal – not illegal – vote should be counted."
Speaking on CNN's State of the Union on Sunday, senior adviser to Mr Biden Symone Sanders dismissed the court challenges as "baseless legal strategies".
Mr Biden received nearly 74.6 million votes to Mr Trump's 70.4 million nationwide and has a 279-214 lead in the Electoral College that determines the presidency.
Mr Biden also leads in Arizona, which has 11 electoral votes, and Georgia, which has 16. If he wins both, he would finish with 306 electoral votes – the same total won by Mr Trump in 2016 when he upset Hillary Clinton.
Only two Republican senators, Mitt Romney and Lisa Murkowski, have congratulated Mr Biden.
Democratic Representative James Clyburn of South Carolina said the Republican Party has a "responsibility" to help convince Mr Trump it is time to give up.
Mr Romney, who voted to convict Mr Trump at his impeachment trial, said the president would eventually "accept the inevitable".
The Utah senator said he "would prefer to see the world watching a more graceful departure, but that's just not in the nature of the man".
But Senator Lindsey Graham of South Carolina, an ally of Mr Trump, said the 74-year-old president should keep fighting.
"We will work with Biden if he wins, but Trump has not lost," Mr Graham said on Fox News. "Do not concede, Mr President. Fight hard."