In this file photo from Wednesday Jan. 6, 2021, Trump supporters beset a police barrier at the Capitol in Washington. Credit: John Minchillo / AP

The U.S. Congressional committee investigating the storming of the Capitol on Jan. 6 is poised to kick off deliberations Tuesday with what is expected to be wrenching testimony from police officers who battled the violent mob of attackers.

After a second Republican lawmaker agreed to join the panel over the weekend, Rep. Bennie Thompson, D-Mississippi, the panel’s chairman, vowed that the committee would work fairly to expose the truth about what happened that “horrible day.”

“We have to get it right,” said Thompson, who has a reputation for working well across the aisle.

By exposing the ugly truth about the Capitol riot, Thompson says he hopes to prevent such an attack from ever happening again.

“(Then) I would have made what I think is the most valuable contribution to this great democracy,” Thompson said.

The controversial committee is empowered to examine what happened on Jan. 6 and what led to the violent attack, which was carried out by supporters of former President Donald Trump hoping to block certification of President Joe Biden’s election win.

It was created by House Democrats after a bipartisan proposal for an independent 9/11-style commission was blocked by Senate Republicans.

The panel will include seven Democrats and two Republicans, Rep. Liz Cheney, R-Wyoming, and Rep. Adam Kinzinger, R-Illinois, both harsh critics of former President Trump.

Pelosi added Kinzinger to the panel on Sunday. GOP Minority Leader Kevin McCarthy earlier yanked his allotted five picks after Pelosi rejected two of them, citing their efforts to downplay the seriousness of the attack.

Despite the partisan drama, Thompson insists the gravity of the task at hand requires him to play it straight and steer clear of party politics.

On the eve of the hearing, Thompson revealed that he initially didn’t believe the severity of the Jan. 6 insurrection when his wife called him to tell him what was happening.

The 73-year-old lawmaker was inside the Capitol, sitting in the upper gallery of the House when his wife, London, frantically called him.

”I’m watching people climbing over the wall right now,” she told him.

Bennie Thompson initially brushed off his wife’s fears.

“I said, ‘You can’t break in. There’s police and barricades and a lot of things out there,’” he recounted.

Within minutes, the reality of the attack was undeniable.

Police rushed Thompson and several dozen other members of Congress to another side of the gallery and told them to duck under their seats as a mob of Trump supporters sought to break into the chamber below.

“It was a horrible day,” said Thompson. “(It’s) still almost surreal that it even occurred.”

Story by Dave Goldiner, New York Daily News