Dr. Jill Biden and retired Gen. Lloyd Austin, President-elect Joe Biden's choice for defense secretary, participated in a care package packing event in Washington D.C. hosted by Operation Gratitude, a nonprofit that sends care packages to members of the military, first responders and their families.

The event marks the last day of box packing in D.C. as part of a multi-day effort in Washington and Los Angeles. Inside the boxes are handwritten letters from volunteers, snacks, hygiene items, handmade items like scarves and bracelets, playing cards and beanie babies.

Biden shared her message for the American people during the holiday season and talked about how her family's holiday plans would be different because of the pandemic.

"I think it's changed every Americans' holiday plans," she said. "You know, families can't be together like they have."

"If all Americans would commit to an act of kindness toward a military family, and, of course so many people are food insecure during this time," she added.

Later, the first lady-elect, Austin and his wife took a photo with the volunteers from Operation Gratitude during which Biden said she was happy to have the Austin's join the Biden family.

"We're so happy to welcome the general to our administration, and we're so proud to have both of them in -- joining the Biden family. So, thank you." she said.

"Great family," Austin added. "Some familiar faces in the crowd. Thank you for all you're doing. God bless you, God bless your families."

-ABC News' Beatrice Peterson and Lauren Lantry

Doug Emhoff, the husband of Vice President-elect Kamala Harris, will serve as a Distinguished Visitor from Practice at Georgetown University Law Center, according to a spokesperson for the transition.

Emhoff, an attorney with nearly 30 years of litigation experience, will also serve as a Distinguished Fellow of the Georgetown Law Institute for Technology Law and Policy, drawing on his expertise in entertainment and media law. He is slated to teach one two-credit course in the spring semester entitled, “Entertainment Law Disputes.”

“I’ve long wanted to teach and serve the next generation of young lawyers,” Emhoff said in a press release from Georgetown. “I couldn’t be more excited to join the Georgetown community.”

The role at the university will be separate and apart from his official role as second gentleman. Emhoff will continue to work with the Biden-Harris transition team to develop the portfolio he will focus on during the upcoming administration.

Emhoff severed ties with his law firm DLA Piper in November. Dr. Jill Biden, one of his predecessors, taught community college students when President-elect Joe Biden served as vice president.

-ABC News' Averi Harper

President Trump tweeted Thursday morning pushing the Supreme Court to rule favorably on the longshot Texas-led case to overturn the election results.

“The Supreme Court has a chance to save our Country from the greatest Election abuse in the history of the United States. 78% of the people feel (know!) the Election was RIGGED,” Trump tweeted.

While not using President-elect Joe Biden’s name, he also posted a tweet insinuating that Biden would be an “illegitimate president” because Biden “lost the election by hundreds of thousands of legal votes in each of the swing states” – a claim which is inaccurate. More votes were cast for Biden than Trump.

The tweets related to election fraud were flagged by the social media platform, with a link stating Trump's claims were disputed.

Meanwhile, Trump on Thursday afternoon plans to have lunch with 12 state attorneys general, 10 of whom have are part of the lawsuit to overturn the election results. Texas’s attorney general, Ken Paxton, who initially filed the lawsuit, was expected to attend.

The meeting comes as the president continues to make a last-ditch effort to overturn the will of the voters and have the already-certified election results in several swing states thrown out.

Asked what would be discussed at the lunch and if the lawsuit would be addressed, White House deputy spokesman Judd Deere said in a statement that “President Trump will have lunch with a dozen state attorneys general and discuss issues important to their citizens and the country, and ways to continue to advance the shared federal-state partnership.”

Per Deere, the expected attendees include attorneys general from Alabama, Arizona, Arkansas, Florida, Indiana, Kentucky, Louisiana, Mississippi, Missouri, South Carolina, Texas and Utah. Mark Brnovich from Arizona and Dan Cameron from Kentucky are the only ones meeting with Trump that have not filed in support of the election lawsuit.

The attorneys general were already in Washington “for a pre-planned meeting,” and the lunch had been “planned around that meeting several weeks ago,” a White House official said. Some Republican attorneys general were already scheduled to be in Washington, D.C. for a separate meeting not affiliated with the White House.

-ABC News' Ben Gittleson

President-elect Joe Biden announced more members of his administration, confirming his picks for secretary of Housing and Urban Development, Agriculture and Veterans Affairs, along with his pick for trade representative and director of the Domestic Policy Council.

Tom Vilsack -- secretary of Agriculture. Vilsack, a two-term governor of Iowa, served as secretary of Agriculture during the entire Obama-Biden administration.

Rep. Marcia Fudge -- secretary of Housing and Urban Development. Fudge has represented Ohio's 11th Congressional District for the last 12 years. If confirmed, she will be the first woman to lead the department in more than 40 years.

Denis McDonough -- secretary of Veterans Affairs. McDonough served as White House chief of staff, deputy national security adviser and chief of staff of the National Security Council during the Obama administration.

Katherine Tai -- U.S. trade representative. Tai currently serves as the chief lawyer on trade for the Ways and Means Committee in the House of Representatives and previously was chief counsel for China trade enforcement in the office of the U.S. trade representative.

Susan Rice -- director of the White House Domestic Policy Council. Rice served as national security adviser under President Obama from 2013-2017 and before that held the position of U.S. ambassador to the United Nations from 2009-2013.

-ABC News' Molly Nagle

Trump and Biden hold dueling events on the pandemic response Tuesday with the president hosting a "vaccine summit" at the White House, just days before a Food and Drug Administration advisory committee holds a hearing on whether to authorize emergency use of a COVID-19 vaccine, while the president-elect is slated to formally roll out his health care picks who will take over handling the COVID-19 pandemic in 43 days.

At his event, Trump is slated to sign an executive order touting his mantra of "America First" that would prioritize Americans’ access to COVID-19 vaccines before the United States helps other countries. But the chief science adviser to "Operation Warp Speed," the U.S. government's initiative to expedite vaccine development which Trump is also expected to tout, said Tuesday morning he doesn't know about the vaccine-related executive order Trump is expected to sign.

"Frankly, I don't know and, frankly, I'm staying out of this. I can't comment," Dr. Moncef Slaoui told ABC News Chief Anchor George Stephanopoulos in an interview Tuesday on "Good Morning America,” when asked to explain the executive order.

The event comes as a senior administration official familiar with the matter confirmed reporting to ABC News that the Trump Administration passed when Pfizer offered in later summer to sell the U.S. more COVID-19 vaccine doses -- an approach which the White House has denied and Slaoui defended Tuesday. Representatives of Pfizer and Moderna -- the two drug companies seeking emergency-use authorization -- are not expected to attend the White House summit, nor is anyone from the Biden transition team.

Biden, meanwhile, is slated to introduce the health care team he will entrust with handling the pandemic California Attorney General Xavier Becerra as Health and Human Services secretary, the first Latino to hold the post if confirmed. Director of the National Institute of Allergy and Infectious Diseases Dr. Anthony Fauci, who is taking on the elevated role of chief medical adviser to Biden in the incoming administration, is expected to dial into Biden’s meeting, though not the one at the White House.

Biden and Vice President-elect Kamala Harris are also meeting Tuesday with several civil rights leaders including NAACP representatives to discuss policy issues around racial equity as well as diversity and representation on the incoming Cabinet. It comes after news leaked that Biden is expected to name retired four-star Army Gen. Lloyd Austin as his defense secretary, who would be the first African American in the post if confirmed, this week.

Tuesday is also the congressionally mandated "safe harbor" deadline -- the date, under federal law, by which the "final determination of any controversy or contest concerning the appointment" of electors "shall be conclusive” -- making it extremely difficult to dispute election results in the courts, where pro-Trump efforts have seen at least 39 defeats to date.