WASHINGTON – In a hearing Tuesday, former law enforcement officials in charge of protecting the U.S. Capitol will discuss how rioters encouraged by former President Donald Trump were allowed to break in Jan. 6 and run amok, attacking police and threatening lawmakers.

Trump's recent impeachment trial ended in acquittal when the Senate fell 10 votes short of the 67 votes needed to find Trump guilty of incitement. It focused on individual injuries, deaths and damage to the Capitol.

"What has not yet been explored in any major, significant way has been the security," said U.S. Sen. Amy Klobuchar of Minnesota, who will oversee Tuesday's hearing as chairwoman of the Senate Rules Committee.

"The only way you do this is to figure out what went wrong," Klobuchar said. "And the only way you do that is getting testimony from the people who were in charge that day."

Klobuchar said three of the four people who will testify Tuesday are no longer on the job. Paul Irving, who had served as sergeant at arms of the House since 2012, resigned the day after the Capitol invasion. So did the Senate's sergeant at arms, Michael Stenger. Capitol Police Chief Steven Sund resigned effective Jan. 16.

The fourth hearing witness will be Robert Contee III, acting chief of the Washington, D.C., Metropolitan Police Force.

All four agreed to testify under oath without subpoenas.

A second hearing in the coming weeks will involve two Senate committees, Klobuchar said, and testimony from officials from the Defense Department, the FBI and the Department of Homeland Security.

Tuesday's hearing will not focus on any roles that law enforcement officers may have played in aiding the rioters, Klobuchar told the Star Tribune. Investigations and discipline of police accused of helping or refusing to confront invaders are going on privately in various departments.

Klobuchar said she will focus on what intelligence services told law enforcement officials before the attack and why it took so long to deploy the National Guard after Trump supporters stormed the Capitol grounds and then the Capitol itself. It was the first large-scale breach of the U.S. Capitol since the British invaded and burned the Capitol in 1814.

"There were reports of bad things about to happen," said Klobuchar, "and it didn't translate into action."

The inability to initially repel Trump's supporters has already cost taxpayers at least a half-billion dollars to pay for enhanced security after the fact. A heavy mesh metal fence 8 feet tall topped with razor wire still encloses the Capitol and the legislative offices of Congress. Tens of thousands of National Guard troops remain deployed to help police protect the buildings.

While the House and Senate seem likely to approve a commission to do an exhaustive investigation of the Capitol attack similar to the commission that deconstructed the Sept. 11 terrorist attacks on the World Trade Center and the Pentagon, Klobuchar believes Capitol security adjustments cannot wait for a monthslong investigative process.

Figuring out when the National Guard should stand down and when — or if — the security fence should be removed are priorities, she said. Another pressing issue is setting entry rules for the Capitol when restrictions ease after the COVID-19 pandemic.

"We have to ensure that this is done in a way that you can still have school trips come to Washington, and they can meet with their senator," Klobuchar said. "There's no way we're going to make this so no one can visit."

Jim Spencer • 202-662-7432