Trump inauguration live updates: Donald Trump moves swiftly to implement his new agenda

While awaiting the Senate confirmation hearing for South Dakota Gov. Kristi Noem, Trump's pick to lead the Department of Homeland Security, Benjamine Carry Huffman has been appointed acting secretary.

Huffman is currently the director of the Federal Law Enforcement Centers, the training arm for federal law enforcement.

Department of Defense official Robert Salesses was also named acting defense secretary until the Senate confirmation hearing is held for Trump's pick, Pete Hegseth.

Salesses is the current deputy director of the Washington Headquarters Service.

The State Department is charging full steam ahead with preparations for Sen. Marco Rubio's first full day as America's top diplomat.

Assuming all goes to plan, two State Department officials say that Rubio -- Trump's nominee to be secretary of state -- will give a speech to mark his arrival on Tuesday. He will also meet both one-on-one and as a group with the foreign ministers of India, Australia, and Japan -- the three countries that, along with the U.S., make up the Quad, a diplomatic partnership seen as critical to countering China's influence in the Pacific.

The Senate is expected to begin working to formally install as many of Trump's nominees as possible and Rubio is expected to come up first. He could be confirmed as soon as this evening.

The flag at the White House has been raised after Trump signed a proclamation for flags to be flown at full staff on all inauguration days.

The flag had been at half-staff following President Jimmy Carter's death on Dec. 29. Trump is ordering the flag to return to half-staff on Tuesday for the remainder of the 30-day period, which began the day of 100-year-old Carter's death.

Last week, House Speaker Mike Johnson ordered that the flags at the Capitol be raised for the inauguration.

With a flurry of executive orders expected today, President Donald Trump's top advisers, including his incoming Department of Justice leadership, are preparing for a storm of legal challenges to some of the most controversial ones.

"We're going to get sued on all of these things," one top Trump adviser said, adding that the volume of litigation is expected to be a full-time job for Trump's DOJ.

Trump has privately told advisers that he believes flooding the zone with executive orders will lead to lawsuits that may be less effective given the volume of actions he plans to take.

During Trump's first administration, he faced upwards of 400 lawsuits challenging his actions. His advisers anticipate more than that this time.

There will be a team inside the Justice Department that is dedicated just to defending Trump's actions in court, sources said.

-ABC News' Katherine Faulders