Incoming White House Chief of Staff Ron Klain gave an overview of the first 10 days of the Biden-Harris administration in a memo to senior staff Saturday shared with reporters.

"President-elect Biden is assuming the presidency in a moment of profound crisis for our nation. We face four overlapping and compounding crises: the COVID-19 crisis, the resulting economic crisis, the climate crisis, and a racial equity crisis. All of these crises demand urgent action," Klain wrote. "In his first 10 days in office, President-elect Biden will take decisive action to address these four crises, prevent other urgent and irreversible harms, and restore America’s place in the world."

The schedule is not comprehensive, Klain noted, but includes:

Jan. 20: Biden plans to ask the Department of Education to extend the pause on student loan payments and interest for Americans with federal student loans, rejoin the Paris Agreement, reverse the "Muslim Ban" (one of Trump's earliest executive orders upon taking office) and issue a mask mandate for federal property and inter-state travel. He will also "take action to extend nationwide restrictions on evictions and foreclosures and provide more than 25 million Americans greater stability."

Jan. 21: Biden plans to sign several executive actions "to move aggressively to change the course of the COVID-19 crisis and safely re-open schools and businesses, including by taking action to mitigate spread through expanding testing, protecting workers, and establishing clear public health standards."

Jan. 22: The president-elect will direct his Cabinet agencies "to take immediate action to deliver economic relief to working families" impacted by the pandemic.

Jan. 25-Feb. 1: Among other executive actions, memoranda and Cabinet directives, Biden plans to sign additional executive actions to address the climate crisis, as well as take steps to "strengthen Buy American provisions," reform the criminal justice system, expand health care access and "start the difficult but critical work of reuniting families separated at the border."

"Full achievement of the Biden-Harris Administration’s policy objectives requires not just the executive actions the president-elect has promised to take, but also robust Congressional action," Klain wrote.

-ABC News' John Verhovek

House Democrats have opened an investigation into what law enforcement and the intelligence community knew about threats to the Capitol ahead of the Jan. 6 siege.

The investigation from the House Intelligence, Oversight, Homeland Security and Judiciary committees will also examine whether anyone with security clearances -- current or former National Security, Defense, Justice or Homeland Security officials -- participated in the riot.

The investigation will also examine the federal law enforcement response in the aftermath of the attack.

"The Committees will conduct robust oversight to understand what warning signs may have been missed, determine whether there were systemic failures, and consider how to best address countering domestic violent extremism, including remedying any gaps in legislation or policy," committee members wrote in a letter to the FBI, DHS and Office of the Director of National Intelligence.

"This still-emerging story is one of astounding bravery by some U.S. Capitol Police and other officers; of staggering treachery by violent criminals; and of apparent and high-level failures -- in particular, with respect to intelligence and security preparedness," the letter later stated.

Democrats plan to request documents and briefings from administration officials as part of the investigation -- just one of several looking into the Capitol attack.

-ABC News' Benjamin Siegel

When Vice President-elect Kamala Harris takes the oath of office at Wednesday's inauguration, the magnitude of her historic election will be marked not only in her remarks but in the details.

The vice president-elect will be sworn in by Justice Sonia Sotomayor, another historic female first. Sotomayor is the first Latina Supreme Court Justice.

Harris, according to a source with knowledge, told ABC News that the vice president-elect was inspired by Justice Sotomayor's background. The pair both previously served as former prosecutors -- Harris in California, Sotomayor in New York.

During her victory speech, Harris weaved in an adage from her mother, Shymala Gopalan Harris, who often told her she would be the first to do many things, but urged her to open doors for others.

"While I may be the first woman in this office, I will not be the last," said Harris.

-ABC News' Averi Harper and Beatrice Peterson

Vice President-elect Kamala Harris on Saturday echoed Biden's message on listening to science as the country faces challenges such as the pandemic and climate change.

"The importance of ... following the science, of listening to the scientists, is clear everywhere we look -- from a pandemic that has taken such a devastating toll, partly because our nation's leaders did not listen to the scientists from the start, to raging wildfires, record-breaking storms and a climate crisis that scientists agree is caused by human beings," Harris said during a press briefing on the administration's science team.

The administration will additionally invest in STEM education "and the next generation of scientists, including women scientists and scientists of color," she said.

Harris also spoke about her personal connection to research as the daughter of a cancer researcher, and she encouraged the next generation of scientists.

"I have a message for all the little girls and boys out there who dream of growing up to be a superhero,” she said. “Superheroes aren’t just about our imagination. They are walking among us. They are teachers and doctors and scientists."

"And you can grow up to be like them, too, so let's dream big, lead with conviction, and see ourselves, each one us, as the superheroes of tomorrow," she added.

-ABC News' Beatrice Peterson, Molly Nagle and John Verhovek

Late Friday, Health and Human Services Secretary Alex Azar refuted several media reports that he was resigning early, but did share his resignation letter -- effective Jan. 20 at noon -- on Twitter.

While Azar wrote on Twitter that it was his "duty to help ensure a smooth transition to President-elect Biden’s team during the pandemic" through Inauguration Day, he did criticize President Donald Trump and called on him to more strongly condemn the violence at the Capitol last week.

"Unfortunately, the actions and rhetoric following the election, especially during this past week, threaten to tarnish these and other historic legacies of this Administration," Azar wrote in the resignation letter. "The attacks on the Capitol were an assault on our democracy and on the tradition of peaceful transitions of power that the United States of America first brought to the world. I implore you to continue to condemn unequivocally any form of violence, to demand that no one attempt to disrupt the inaugural activities in Washington or elsewhere, and to continue to support unreservedly the peaceful and orderly transition of power on January 20, 2021."

Azar clarified he handed in the letter, dated Jan. 12, last week "along with every other political appointee."

The two-page letter, in which he calls serving as HHS secretary "the greatest professional privilege and honor of my life," details the administration's response to the coronavirus pandemic. Azar paints an entirely rosy picture, referring to it as a "remarkable response," despite skyrocketing deaths and case rates across most of the nation.

"While we mourn every lost life, our early, aggressive, and comprehensive efforts saved hundreds of thousands or even millions of American lives," he wrote, echoing a refrain from the president. There have been over 391,000 deaths in the U.S., nearly twice the number of the second-highest country (208,000 in Brazil).

He also highlighted the agency's efforts to combat the opioid crisis, electronic cigarettes and the HIV epidemic, and made special mention of "protect[ing] the sanctity of human life from conception to natural death."

Azar has served as HHS secretary since January 2018. President-elect Joe Biden has nominated Xavier Becerra, California's attorney general, to serve as his HHS chief.

ABC News' Ben Siu contributed to this report.