The officer stood dead smack in the middle of the floor of the United States Senate. Across his chest, an orange POLICE sash. Hanging from his right shoulder, a semiautomatic weapon.

He said barely a word, just stared straight ahead at the backdoor entrance to the Senate Chamber.

It was 2:15 p.m. Wednesday and the U.S. Capitol was under assault, the most brazen attack on Congress since terrorists hijacked an airplane and attempted to slam it into the building more than 19 years ago. On Wednesday, a pro-Trump mob crashed into the building in a historic first that sent Washington into lockdown and prompted the type of evacuation that congressional security officials have been planning since 9/11 but had never had to execute.

Moments before, I had been sitting in the Senate press gallery high above the Senate floor, watching Senate Minority Leader Charles E. Schumer (D-N.Y.), Senate Majority Leader Mitch McConnell (R-Ky.) and other senators debate Republicans’ unfounded objections to counting the electoral college votes that would seal President-elect Joe Biden’s convincing victory over President Trump.

Suddenly, Vice President Pence, who had been presiding over the chamber from the Senate dais, got a signal that it was time to move.

A growing mob outside had breached the barricades and entered the Capitol. Pence was quickly ushered away by Secret Service agents.

I bolted out of the press gallery hoping to find out whether Pence just needed a bathroom break from the tedious proceedings. I bounded down the stairs to the second floor, where senators enter and exit the Chamber. Then I heard it: Police clashing with rioters yet another floor below. I could hear a loud thwacking sound — possibly a billy club being wielded against the invaders.

I retreated back up to the third-floor press gallery in time to see Sen. Kyrsten Sinema (D-Ariz.) finish defending her state’s electoral count for Biden. Then Capitol Police and staff ordered everyone into the Senate Chamber.

For our own safety.

Trump supporters overtook Capitol Police officers to enter the building as lawmakers attempted to count the electoral college votes on Jan. 6. (The Washington Post)

I was ordered into a gallery that is reserved for family and close friends of senators — Rep. Greg Pence (R-Ind.), the vice president’s brother, had just been there watching the proceedings. But I climbed over several rails and chairs to get back to the usual press location, directly above where Pence had been sitting as the presiding officer.

Soon, the Senate was sealed off and the session was adjourned. Capitol Police raced around the two-story Senate Chamber locking every set of doors.

Then Sen. Amy Klobuchar (D-Minn.) looked at her phone and announced: “Shots fired.”

A veteran Capitol Police officer tried to calm the senators, telling them the report might not be accurate. But at 2:30 p.m., police ordered everyone out.

In the most dramatic moments of the siege, with armed officers in every corner of the Senate, police began barking out instructions. They marched us all — a phalanx of senators, staff and press — through multiple office buildings in search of the safest grounds to shelter on the Capitol complex.

We didn’t know it at the time, but a similar scene was playing out on the other side of the Capitol, where the House Chamber was evacuated and lawmakers ran for cover in a secure location on their side of the building.

We were not allowed to take the stairs, because the mob was on the floors below. So into the elevators and down to the basement we went, racing toward the Capitol Visitor Center. The CVC is a vast underground bunker of a structure that finally got built after 9/11. It cost roughly $700 million and has multiple secure rooms and blast-resistant doors.

An officer, holding back two doors, ordered us to head toward the Russell Senate Office Building because the pro-Trump mob had also breached the CVC.

Some senators ran; some walked. Security guards held Schumer by the shoulders to whisk him along.

In a sign of quick staff thinking, aides to the Senate parliamentarian rounded up several people to grab the boxes containing the electoral college certificates submitted by the states — documents needed to certify Biden’s victory.

By 2:45 p.m. most senators and a collection of aides and media had gathered in the secure room. An officer informed us that we were safe but said it would take a while to secure the complex. In the meantime, they said they were trying to find buses to get us to safer ground.

Back in the Capitol, police began a room-by-room search to find senators, staff and reporters who had been left behind. One senior GOP aide, who has an office not far from the Senate floor, said he took a steel rod and barricaded his door when the pro-Trump mob approached. For what seemed like 20 minutes, he said, rioters banged on his door, trying to break in.

Others huddled in silence in small rooms with doors locked and cellphones turned off while the rioters walked past.

Inside the Senate’s secure location, one senior officer ordered a set of underlings to go secure Sen. Tammy Duckworth (D-Ill.), a double amputee who lost both legs while serving in the Iraq War. A recipient of the Army Commendation Medal for her service flying Black Hawks, she hid in her office three floors above, unwilling to any strangers in. The senior officer gave specific instructions of what to yell: “Senator Duckworth, Senator Klobuchar said come to the door.”

A few minutes later, she appeared in the secure spot.

Somehow, Capitol food service operations still appeared to be up and running through the melee. At 4 p.m. and 5 p.m., hundreds of box lunches and bottles of water were rolled into the holding spot. Senators, staff, media and police wielding automatic weapons grabbed lunches of chicken and beef.

Eventually, reporters were herded out of the main secure room and into an outside lobby. Senators stayed behind, and began discussing what had gone wrong with the basic fabric of American democracy. Televisions were wheeled into the senators-only room so they could watch the chaos unfold for themselves.

Pressure mounted on the few Republicans who had been objecting to counting Biden’s electoral college votes, giving life to the mob’s delusions of four more years for Trump. Just before 5 p.m., Sen. Ted Cruz (R-Tex.) led a contingent of GOP objectors into a separate room to discuss whether to go forward with their challenge in light of the mob violence.

Around 6 p.m., more senators began talking about returning to the Senate floor in a show of democratic force — an idea that echoed a decision by many members to return to the Capitol’s East Front steps the night of the 2001 terrorist attacks. On that night, in a show of bipartisan support, Republicans and Democrats stood together and sang “God Bless America.

At the other end of Pennsylvania Avenue, Trump blamed lawmakers for the chaos. “These are the things and events that happen when a sacred landslide election victory is so unceremoniously and viciously stripped away,” he tweeted.

A few minutes later, Sen. Tommy Tuberville (R-Ala.) walked past reporters. He was asked what he thought about Trump’s statement but walked away, saying nothing.

Just before 6:45 p.m. — four hours after senators fled the Capitol — loud applause echoed from the secure room. Congress had decided to reconvene.

As our group trekked back to the Capitol, someone shouted “make way, make way.”

Nonpartisan staffers from the parliamentarian’s office were carrying the boxes containing the electoral college votes back to the Senate.

Biden would still be declared the winner.