Biden fractures foot after fall, will likely be in walking boot 'for several weeks'

Despite telling reporters Thursday that he would leave the White House if Biden is inaugurated, while still not conceding, Trump continued on Friday to baselessly cast doubt on the president-elect's record-breaking popular vote lead.

In a tweet Friday morning, Trump wrote, "Biden can only enter the White House as President if he can prove that his ridiculous "80,000,000 votes" were not fraudulently or illegally obtained" and went on to allege -- without citing any proof -- that Biden "got a big unsolvable problem!"

As reported previously by ABC News, the Trump campaign and its allies have lost at least 30 cases brought in the effort to overturn the results of the election, according to an ABC News count. 

Biden won the Electoral College by the same margin as Trump did in 2016 and leads in the popular vote by over 80 million votes. 

-ABC News’ Alisa Wiersema

Several leading candidates for the roles in president-elect Joe Biden’s administration have come under scrutiny for their work in corporate America or lobbying history.

Michele Flournoy, a leading candidate for the head of the Department of Defense after serving in senior posts at the Pentagon during the Clinton and Obama administrations, has faced criticism from progressive and left-leaning activists for her ties to defense contractors and a strategic advisory firm that has faced questions about its clients.

Several other Cabinet selections and initial White House hires for the Biden administration, along with members of his transition efforts, are under the microscope as well, showing an early struggle between the activist and established wings of the Democratic Party, which collaborated to elect Biden and deny President Donald Trump a second term.

-ABC News’ Benjamin Siegel and Soo Rin Kim

Vice President Mike Pence shared a message of gratitude on Thanksgiving to first responders, military members and health care workers.

“On this Thanksgiving Day, we’re thankful for our Family, Friends & the Doctors, Nurses, First Responders & Men & Women of our Armed Forces that we’ve met along the way. God Bless our Healthcare Workers & our Military, especially those deployed overseas Defending Our Freedom!”

In a message earlier Thursday, the Pence family wished everyone a Happy Thanksgiving on behalf of the vice president and second lady Karen Pence.

After wrapping his teleconference with troops, Trump spoke with reporters. It was the first time he's answered questions since Biden declared victory. 

The president delivered a lengthy list of grievances and unfounded claims of election fraud across the country. 

"It's going to be a very hard thing to concede because we know there was massive fraud," Trump said.

The president provided no direct evidence of fraud while claiming irregularities in Pennsylvania, Michigan and Wisconsin skewed the results in Biden's favor.  He also, again, went after Dominion Voting Systems. 

When asked whether he would announce a run in 2024 if Biden occupies the White House on Jan. 20, the president said, "I don't want to talk about 2024."

Asked if he would leave the White House if Biden is inaugurated, Trump responded, "Certainly, I will. And you know that."

He was also asked whether he would attend Biden's inauguration as tradition dictates.

"I don't want to say that yet. I know the answer, I'll be honest, I know the answer but I just don't want to say it yet," he said.

- ABC News' Liz Alesse