Michigan state legislature closes offices due to 'credible threats of violence'

Ahead of introducing his health care picks, Biden made his mask campaign official and called on all Americans to wear a mask for the first 100 days of his presidency as part of three key objectives he's asking his health care team to complete in his first 100 days in office.

"My first 100 days won’t end the COVID-19 virus. I can't promise that," Biden said. "We didn’t get into this mess quickly. We're not going to get out of it quickly. It's going to take some time. But I'm absolutely convinced that in 100 days we can change the course of the disease and change life in America for the better."

Biden said his team's second initiative is to have "at least 100 million COVID vaccine shots into the arms of the American people in the first 100 days." The initiative comes as the Biden team has said it's seen "no detailed plan" on vaccine distribution from the Trump administration.

Finally, Biden said getting children back to school and keeping them in school will be a "national priority" for the team in the first 100 days, saying Congress can help make this happen with the appropriate funding.

"I'm encouraged by the bipartisan efforts in Congress around a $900 billion economic relief package which I've said is critical, but this package is only a start for more action early next year," Biden added.

Biden is introducing a slate of health care experts and officials who will lead his administration's response to the ongoing COVID-19 crisis.

"Today, I’m very proud to be announcing our health care and COVID team at a critical time, as we near the end of one of the toughest years we've faced as a nation," Biden said, adding this group of "world class experts" will be "ready on day one."

California attorney general and former California congressman, Xavier Becerra, is Biden's nominee for secretary of Health and Human Services. If confirmed, he would be the first Latino to lead the department.

Vivek Muthy has been nominated to be U.S. surgeon general, a role he served in during the Obama administration.

Dr. Rochelle Walensky, a leading expert on virus testing, prevention and treatment, is nominated to serve as director of the Centers for Disease Control and Prevention.

Dr. Marcella Nunez-Smith, one of the country’s foremost experts on health care disparities, will serve as the COVID-19 equity task force chair.

As Biden said last week, Dr. Anthony Fauci will stay on in his current role as as director of the National Institute of Allergy and Infectious Diseases and will take on the elevated role of Biden's chief medical adviser on the COVID-19 pandemic.

Jeff Zients will serve as coordinator of the COVID-19 response and counselor to the president, and Natalie Quillian will serve as deputy coordinator of the COVID-19 response.

During first speech post-election on immigration, Vice President-elect Kamala Harris’ told immigration activists that she's focused on working to “right the wrongs of these past four years."

Harris, during pre-taped remarks at the 13th Annual National Immigrant Integration Conference, ticked off a few immigration-related actions the Biden administration hopes to tackle in the first 100 days in office. 

“In our first 100 days, we will send an immigration bill to Congress, reinstate DACA, repeal harmful and discriminatory policies like the Muslim ban, and during our administration, we will repeal indiscriminate enforcement policies that tear families apart and make us less safe," Harris said. 

The daughter of two immigrants, Harris later noted the sacrifice that immigrants have made during the pandemic as essential workers, vowing to create a “humane immigration system.”

-ABC News' Beatrice Peterson

Trump reached out to Pennsylvania State Speaker of the House Brian Cutler last week asking about the legislature possibly overturning the election as part of his ongoing and apparent pressure campaign to have GOP-controlled legislatures flip results in his favor in battleground states he lost. 

Mike Straub, a spokesman for Cutler, confirmed to ABC News reporting in The New York Times that Trump asked what options were available to the legislature on the phone call.

“Cutler made it very clear what power the legislature has and does not have," Straub told ABC News, adding he is "not aware of the President explicitly asking to turnover [sic] the election results."

Straub separately told ABC News that he was not present for the conversations between Cutler and the president, but he was briefed. 

"The president wanted to know what options were available to the legislature to address those concerns... Speaker Cutler was very clear in explaining what power the legislature has and does not have within our state Constitution," Straub said. "One remedy the Trump campaign is seeking in a court case involves the legislature seating electors -- Speaker Cutler explained the legislature does not have that authority."

Cutler separately signed onto a resolution last week imploring Pennsylvania Republicans in Congress to officially contest the election results in January. While this has happened in the past, including over the election of George W. Bush, it is highly unlikely to overturn the election results.

The Supreme Court may decide Tuesday to take up a challenge by Pennsylvania Republican Rep. Mike Kelly over the constitutionality of mail-in voting, but legal experts have told ABC News that is a long shot. With Tuesday being the constitutionally mandated "safe-harbor" deadline for electors, all legal challenges are meant to be resolved by the end of the day, thus ensuring the correct electors will cast their votes in statehouses on Dec. 14.

-ABC News' Alex Hosenball