There is a preliminary plan to close the entire National Mall to the public for Inauguration Day amid security concerns, ABC News has confirmed.

The Washington Post was the first to report on the development, but The National Park Service has said it will make an announcement on the Mall following ongoing discussions with the Secret Service, the Biden Inaugural team and D.C. Mayor Muriel Bowser.

Traditionally, members of the public gather on the National Mall -- bookended by the Capitol building and Lincoln Memorial -- for viewing of the inauguration on large jumbotrons.

But the Mall's potential closure comes in the wake of a violent seige on the U.S. Capitol building last week, which left at least five people dead, and amid heightened security concerns regarding armed protests being planned ahead of Biden's inauguration on Jan. 20.

Security preparations for next week have already increased with up to 20,000 National Guard troops authorized to provide security at the Capitol and around Washington, D.C., for next week's ceremony, according to a Defense Department official.

Bowser has already warned visitors to stay away from the District for the inauguration due to threats of both the coronavirus pandemic and of violence.

Editor’s Note: A previous version of this post reported that the entire National Mall would be closed to the public for Inauguration Day amid security concerns. The text has been updated to reflect the fact that the closure is only a preliminary plan.

-ABC News' Dee Carden and Josh Margolin

Arizona Gov. Doug Ducey, a Republican, has announced he will attend Biden’s inauguration after weeks of attacks from Trump for signing the certification of Arizona's election results affirming Biden's narrow win in the state.

“It doesn't matter who you supported in the election — once the election is over, we put country before party. Never has it been more important than right now to observe these traditions for the whole world to see," Ducey said in a statement Thursday.

"I was honored to represent Arizona at the inauguration of President Trump in 2017, and I am honored to represent our state at the 59th Inaugural Ceremonies next week. President-elect Biden is assuming office at a critical time in our nation’s history, and I wish him well," he added.

The Arizona Republican Party is scheduled to meet a few days later on Jan. 23, when members will vote on censuring some apparent party foes including Ducey, Cindy McCain and former Sen. Jeff Flake, R-Ariz.

-ABC News' Meg Cunningham

On one side of Pennsylvania Avenue in Washington, D.C., President Trump -- now the only president in history to be impeached twice -- faces another Senate trial following the House charging him Wednesday with one article of impeachment for "incitement of insurrection." Shortly after 10 Republicans sided with Democrats for the vote, Trump released a video from the Oval Office condemning the violence at last week's Capitol riot, which he called a "calamity," but he did not address impeachment.

On the other side of Pennsylvania Avenue stands what's now become a crime scene -- the U.S. Capitol complex. By this weekend, up to 20,000 National Guard troops, many armed, will be deployed to the area amid heightened security concerns and ahead of Biden’s inauguration. Inside the Capitol, metal detectors were installed to enter House chamber earlier this week, and House Speaker Nancy Pelosi announced plans to fine members who don't comply with the new protocol up to $5,000.

Senate Majority Leader Mitch McConnell signaled Wednesday that Trump's Senate trial should take place after Trump leaves office, saying he wouldn't call back the Senate ahead of its Jan. 19 return. McConnell also indicated Wednesday he's considering voting to convict the president, issuing a statement that says he has "not made a final decision." Pelosi has not publicly announced her timeline, but a source involved with deliberations told ABC News Wednesday she plans to send the article to the Senate next week.

Biden, reacting to Trump’s second impeachment late Wednesday, expressed his hope that the Senate will be able to maintain a bifurcated schedule, allowing the trial to move forward along with his agenda -- a message his transition has been consistent on this week. But Democrats are facing the reality that Trump is still likely to loom large over Biden's first days in office.

On Thursday evening, Biden is slated to deliver remarks on the public health and economic crises from Wilmington, Delaware, and introduce his COVID-19 vaccine and economic relief proposal. Vice President-elect Kamala Harris is expected to join.

There are no public events on Trump’s schedule.

With Trump facing a Senate trial as soon as next week, he has no organized defense team as his top lawyers have refused to represent him.

White House counsel Pat Cipollone, his deputies, and outside lawyers Jay Sekulow, and Jane and Marty Raskin are not expected to be involved.

Trump has been increasingly irritated with his personal attorney Rudy Giuliani and hasn’t been taking his calls, according to sources familiar with the matter, though Giuliani has been spotted in the West Wing recently.

And former Harvard professor Alan Dershowitz is not on board yet, though aides to the president have had discussion with him about joining the team.

Another attorney, John Eastman, whose extremist positions have troubled some members of the president’s legal team recently, is expected to take some sort of role in Trump’s impeachment defense.

Eastman represented the president in the Texas dispute and has previously pushed a racist conspiracy theory about Vice President-elect Kamala Harris.

Trump has asked top aides about how a Senate trial would look this time around. As he did during his first impeachment, Trump raised the idea of testifying himself, which aides dissuaded him from pursuing.

-ABC News' Katherine Faulders and John Santucci

As procedural votes were underway in the House, Speaker Nancy Pelosi went outside the Capitol to thank the National Guard troops deployed to the complex in the wake of last week's riot and ahead of Biden's inauguration in one week.

Some National Guard members inside the Capitol were spotted taking in the sights of the Rotunda Wednesday morning, gathering around and listening to Rep. Brian Mast, R-Fla., an Army veteran who lost both legs in Afghanistan.

The Capitol has been closed to tours for months due to the coronavirus pandemic. With the exception of last Wednesday's attack, this is one of the few times visitors have snapped photos inside the building during the pandemic -- finding themselves with unique access as they've been designated to protect the building and lawmakers.

As lawmakers arrived on the Hill ahead of the House gaveling in to consider Trump's second impeachment, a heavy National Guard presence greeted them both outside and inside the building -- with some resting, embracing their rifles, on the floor of the Capitol.

Jane Campbell, the president and CEO of the United States Capitol Historical Society, confirmed to ABC News that troops have not been quartered in the Capitol since the Civil War -- when the Rotunda was still under construction, and the open-air space was used as a field hospital.

A Defense official said the National Guard members seen sleeping at the Capitol are on breaks and noted that it’s not uncommon on domestic or overseas deployments to see members taking breaks in between long shifts.

There are currently 6,600 members of the National Guard in Washington, D.C. with more continuing to flow in. A Defense official said Wednesday afternoon that the National Guard has now been authorized to have up to 20,000 Guardsmen in Washington for inauguration security and that most may be in town by this weekend.

-ABC News Luis Martinez and Benjamin Siegel