Rep. Liz Cheney says Trump sat in the White House dining room and watched the Capitol riot unfold on TV instead of taking immediate action to stop the violence

• Trump watched the Capitol riot unfold on TV and resisted taking immediate action, Rep. Liz Cheney said.
• "The president could have at any moment ... gone on live television, and told his supporters who were assaulting the Capitol to stop," she said.

The House Select Committee investigating the January 6 Capitol riot has "firsthand testimony" that former President Donald Trump watched the violence unfold on television instead of taking immediate action to stop the attack, Rep. Liz Cheney said on Sunday.

"We are learning much more about what former President Trump was doing while the violent assault was underway. The committee has firsthand testimony now that he was sitting in the dining room next to the Oval Office watching the attack on television as the assault on the Capitol occurred," Cheney, vice chair of the panel, told ABC News' George Stephanopoulos.

The Wyoming Republican called Trump's conduct that day "a dereliction of duty."

"We know, as you know well, that the briefing room at the White House is just a mere few steps from the Oval Office. The president could have at any moment walked those very few steps into the briefing room, gone on live television, and told his supporters who were assaulting the Capitol to stop. He could have told them to stand down. He could have told them to go home, and he failed to do so," she said.

The January 6 committee also has firsthand testimony that members of Trump's staff, including his daughter and then-White House senior advisor, Ivanka Trump, "went in at least twice to ask him to please stop this violence," Cheney said.

Prior to the investigation's findings, several news reports last year highlighted that Trump watched the riot on television and did not take steps to intervene.

Just five days after the riot, The Washington Post reported that Trump was glued to the TV screen as members of Congress locked down in the Capitol sought his help.

Post reporter Carol Leonnig, co-author of the book "I Alone Can Fix It," described Trump as "almost giddy" while he watched the riot on television. Journalists Bob Woodward and Robert Costa also reported in their book "Peril" that Trump ignored pleas to step in and instead continued watching the attack on TV.

Hours afterward, Trump released a video urging his supporters to go home while also telling them: "We love you, you're very special." Twitter and Facebook later suspended Trump from their platforms due to further risks of violence.

"It took Trump 187 minutes to make a statement calling off the mob that attacked our Capitol," the January 6 committee tweeted on Monday. "The former President's dereliction of duty is cause for serious concern."