America's most senior military leaders condemned the violent invasion of the US Capitol last week and reminded service members of their obligation to support and defend the Constitution and reject extremism in a statement that underscored the unprecedented challenges facing the country in the aftermath of the January 6 insurrection attempt by President Donald Trump's supporters.

"We witnessed actions inside the Capitol building that were inconsistent with the rule of law. The rights of freedom of speech and assembly do not give anyone the right to resort to violence, sedition and insurrection," said the statement, released Tuesday and signed by America's most senior general, Mark Milley, and the entire Joint Chiefs of Staff, which is comprised of the heads of each military branch.

The extraordinary statement underscores the scale of the challenge and the depth of the uncertainty and concern in Washington, where officials across the US security establishment scramble to deal with the aftermath of the chaos at the Capitol, and around the country, as all 50 states are preparing for possible violence.

At the same time, federal officials are determining how best to protect lawmakers in the seat of American democracy, as more information comes to light about Trump supporters' plans to stage another attack and disrupt the inauguration of President-elect Joe Biden.

These efforts are underway across security agencies at federal and local levels as Washington's political drama continues to unfold. The House is expected to vote Wednesday on Trump's second impeachment, as significant cracks began appearing in GOP support for the President.

The President, meanwhile, insisted on Tuesday that he believes he bears no responsibility for the insurrection carried out by his supporters and has yet to explicitly call on them to refrain from launching another assault on the Capitol.

As Washington readies for any possibility, officials there unveiled security efforts ranging from immediate and concrete steps by the US Capitol Police, which announced road closures around the Capitol that will last indefinitely, to a massive forensic effort by the Justice Department to reconstruct the events of January 6 and the perpetrators behind crimes committed that day.

Federal investigators told reporters Tuesday the scope and the scale of that wide ranging probe is unprecedented in FBI and Justice Department history and is creating a picture of the insurrection that will "shock" people. That work unfolds even as investigators say they are also focused on preventing future attacks.

Lawmakers, deeply shaken by the hours of violence last week, are discussing steps to protect themselves, citing Republican members who may have cooperated or communicated with the rioters and other Republican colleagues who carry guns into the Capitol against the regulations.

The Capitol Police set up metal detectors outside the House floor as of Tuesday afternoon and all House members, staffers and aides will have to go through them, an aide and a US Capitol Police source told CNN.

Maryland Sen. Chris Van Hollen emerged from an all-senators briefing on inaugural security to tell CNN that the numbers people expected to come to Washington next week and the potential for them to be violent -- particularly the militia extremists among them -- is "scary."

Van Hollen told CNN he's "confident" that "everybody will be fully prepared" and that the security arrangements put in place for the event amount to "an all-of-government approach. They are throwing everything we got to make sure we have a successful inauguration at the point."

Administration officials from across government were scheduled to convene for a major interagency "requirements" meeting Tuesday afternoon to discuss in depth security requirements for the inauguration and the concerns that some events in Washington, DC, could turn violent, multiple senior defense officials told CNN.

The Joint Chief's statement Tuesday reminding troops of their obligation to defend the Constitution is a disturbing indication of their concern -- the chiefs seek, wherever possible, to avoid taking stances that may have political overtones. But the military leaders felt it was important to make a statement given the gravity of events surrounding the inauguration, CNN was told.

"As Service Members, we must embody the embody the values and ideals of the Nation. We support and defend the Constitution. Any act to disrupt the Constitutional process is not only against our traditions, values, and oath; it is against the law," the statement said.

The statement referenced the certification of the election by Congress and said, "President-elect Biden will be inaugurated and will become our 46th Commander in Chief."

The statement comes as the military has launched an effort to examine whether some in the ranks of the military may be sympathetic to the aims and extremist beliefs being propagated by some Trump supporters.

The US Army is working with the Secret Service to determine if there are soldiers who will be part of the National Guard contingent providing security at Biden's inauguration who require additional background screening.

The DC National Guard is also providing additional training to service members as they arrive in Washington to stress that if they see or hear something that is not appropriate, they should report it to their chain of command, an Army spokesperson said in a written statement to CNN.

"There is no place for extremism in the military and we will investigate each report individually and take appropriate action," the spokesperson said.

"The Army is committed to working closely with the F.B.I. as they identify people who participated in the violent attack on the Capitol to determine if the individuals have any connection to the Army," the statement said while adding that any type of activity that "involves violence, civil disobedience, or a breach of peace," may be punishable under the Uniform Code of Military Justice or under state and federal law.

Current Defense Department policy requires all service members be trained annually under a program that requires department personnel to report "any information regarding known or suspected extremist behavior that could be a threat to the department or the United States," the statement said.

Officials from the FBI and Justice Department compared their investigation of January 6 to terrorism probes.

"People are going to be shocked by some of the egregious contact that happened in the Capitol," acting US Attorney Michael Sherwin said at a press conference Tuesday, in a reference to assaults by rioters on federal and DC police officers.

"So the picture is going to build. I think there's a lot of misconceptions about what happened within the Capitol, and it's going to come into laser focus I think over the next weeks and days," he added.

"The FBI is quite familiar with large-scale, complex investigations ... we are up to the challenge," FBI Washington DC field office assistant director Steven D'Antuono said.

Sherwin echoed that point, telling reporters, "The scope and the scale of this investigation into these cases are really unprecedented not only in FBI history but probably DOJ history."

"The Capitol grounds outside and inside are essentially a crime scene," he said. "It is not going to be solved in the coming months," he added. Sherwin said he has given his prosecutors "marching orders" to pursue significant sedition and conspiracy cases related to the insurrection.

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