General Services Administration chief Emily Murphy, a Trump appointee who has the sole authority to green light Biden's formal transition, has not signed an "ascertainment" that would allow Biden's team to contact federal agencies ahead of the President-elect's inauguration in January.
Ron Klain, Biden's choice as White House chief of staff, told ABC'S This Week that the first Biden cabinet picks would come tomorrow. Biden won Pennsylvania by more than 80,000 votes.
President-elect Joe Biden will announce the first of his Cabinet appointments on Tuesday and is planning for a scaled-down inauguration due to the coronavirus pandemic, aides said on Sunday, as he lays the foundation for his new administration despite President Donald Trump's refusal to concede.
Maryland's Republican Governor Larry Hogan told CNN's State of the Union: "We're beginning to look like a banana republic".
Trump vowed to appeal in a tweet late Saturday night. "Thank you!" the president tweeted, following Friday's disclosure that the 42-year-old Trump scion had become one of the almost 12 million Americans infected by the virus.
In his ruling, Brann described Trump's case as "strained legal arguments without merit and speculative accusations", characterizing the incumbent U.S. president's lawsuit as "Frankenstein's monster".
Even Fox News host Tucker Carlson, who had been one of Mr Trump's staunchest supporters, challenged the campaign's legal team to provide proof of widespread fraud. The move is unlikely to stop Pennsylvania from certifying President-elect Joe Biden's victory in the state as soon as Monday.
Trump's campaign told a judge it was appealing the ruling by US District Judge Matthew Brann to the US 3rd Circuit Court of Appeals, a day before the state's 67 counties are set to certify their results and send them to state officials. "She is not a member of the Trump Legal Team". Trump took to his Twitter page to condemn Biden for doing so without his concession, still stating that investigations into the validity of the mail-in votes from the aforementioned states still pending.
Mr Trump has already started lobbying legislators, including Michigan's senate majority leader, Mike Shirkey and the state's house speaker, Lee Chatfield - but to no avail.
The Electoral College is due to formally vote on December 14, with certifications to take place beforehand.
Attempts to thwart certification of vote tallies have failed in courts in Pennsylvania, Georgia, Michigan and Arizona.
President Trump's legal team on Sunday filed an appeal to a federal judge's ruling that struck down his campaign's effort to block the certification of votes in Pennsylvania.
It is separate from the @realDonaldTrump Twitter account and the @DonaldTrump Facebook page that U.S. President Donald Trump mostly uses to write his posts.
They requested a two-week delay to allow a full audit of results in Wayne County.
Biden won the state by 2.8 percentage points but the Republican National Committee and the state Republican Party want state officials to investigate alleged ballot irregularities in Wayne County, the state's largest, and home to the city of Detroit. Michigan's canvassing board, which is evenly split between two Democrats and two Republicans, will meet on Monday to decide whether to certify the results. But Republican Secretary of State Brad Raffensperger has reiterated confidence in the results, and in a Saturday opinion piece in the Washington Post he said: "Georgia's voting system has never been more secure or trustworthy".
Two of Trump's former national security advisors - he fired both unceremoniously - warned that the president's actions questioning the vote's legitimacy could have negative ramifications for the Republican Party and the country.
During the campaign, Biden severely criticised Trump's go-it-alone foreign policy and pledged to recommit to North Atlantic Treaty Organisation and other global pacts, while promising to tap experts to fight the Covid crisis and other problems at home.