Ahead of Biden's inauguration and in the wake of last week's attack at the Capitol, the United States Capitol Police (USPS) has enhanced security measures across the Capitol Complex, including adding fencing and making several street closures until further notice, the agency announced Thursday.

"Be advised that the U.S. Capitol Complex is closed to the public, and the Capitol Grounds will not be accessible to the public on January 20, 2021.  Anyone attempting to unlawfully gain access to the Capitol Grounds by climbing a fence or any other unlawful means will be subject to an appropriate use of force and arrest," the USPS said in a statement.

Workers were seen installing barbed wire on security fencing surrounding the Capitol on Thursday afternoon as National Guard troops, some armed, patrolled the area. As National Guard troops continue flowing into the area, there are currently over 7,000 currently stationed in Washington with that number expected to grow to 20,000 over the weekend.

-ABC News' Jake Date and Luis Martinez

House Minority Leader Kevin McCarthy, R-Calif., does not support efforts to remove Rep. Liz Cheney, R-Wyo, as House GOP conference chair and a member of House GOP leadership, a McCarthy spokesman told ABC News. This comes after some conservative House Republicans called on her to step down following her announcement that she supported impeaching Trump.

The Wyoming Republican and daughter of former Vice President Dick Cheney is the highest-ranking woman in Republican leadership and was reelected to by GOP members at the start of this Congress.

"We ought to have a second vote," Rep. Jim Jordan, R-Ohio, told reporters Wednesday about the leadership position. "The conference ought to vote on that."

"She should not be serving this conference," Rep. Andy Biggs, R-Arizona, said Tuesday.

On Wednesday night she joined nine other House Republicans in breaking from the party and voting to impeach Trump for his role in last week's riot at the Capitol.

-ABC News' Benjamin Siegel

Republican Sen. Lisa Murkowski of Alaska said in a statement Thursday she believes that the House responded to Trump's actions "appropriately" by impeaching him but does not say how she will vote.

"On the day of the riots, President Trump’s words incited violence, which led to the injury and deaths of Americans – including a Capitol Police officer – the desecration of the Capitol, and briefly interfered with the government’s ability to ensure a peaceful transfer of power. Such unlawful actions cannot go without consequence and the House has responded swiftly, and I believe, appropriately, with impeachment," she said in a statement.

Murkowski said she intends to hear arguments in the Senate before deciding whether she will vote to convict.

"I will follow the oath I made when sworn as a U.S. Senator. I will listen carefully and consider the arguments of both sides, and will then announce how I will vote," Murkowski said.

It's also unclear how Republican Majority Leader Mitch McConnell will vote in the Senate trial, telling Republican colleagues in a memo Wednesday he hasn't "made a final decision" on whether to vote to convict Trump.

-ABC News' Allison Pecorin

Five key Senate panels have now confirmed that they will hold confirmation hearings for Biden's top national security officials before Inauguration Day -- although it remains unlikely most of his picks will be confirmed by day one.

Avril Haines will have her hearing Friday to be Director of National Intelligence, while four others will have theirs on Tuesday -- Tony Blinken for secretary of state, Janet Yellen for Treasury secretary, Lloyd Austin for Defense secretary, and Alejandro Mayorkas for Homeland Security secretary.

The Senate Foreign Relations Committee hasn't scheduled a hearing yet for Linda Thomas-Greenfield, Biden's pick for U.N. ambassador and a member of his Cabinet, despite her being announced in November. Bill Burns, Biden's pick to be CIA director, also doesn't have a hearing scheduled yet, but Biden only announced his intention to nominate Burns Monday.

It's unclear how long after a confirmation hearing any of these Cabinet picks can be confirmed, especially with an impeachment trial -- but they'll require a committee vote and then a full Senate vote. It's likely most won't be confirmed and in position on Inauguration Day.

Biden's team has escalated pressure this week to confirm his national security Cabinet as soon as possible.

In contrast, on Trump's Inauguration Day, the Senate confirmed both John Kelly as Department of Homeland Security secretary and Jim Mattis as Department of Defense secretary, and 11 more Trump nominees already had their confirmation hearings. President Barack Obama had seven Cabinet chiefs confirmed on Inauguration Day, while six more had confirmation hearings by then and his Defense Secretary Bob Gates stayed on from the Bush administration, according to the U.S. Senate website.

-ABC News' Conor Finnegan and Molly Nagle

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