An eyewitness who was thought to be in the room with Mr Trump and his eldest daughter that day told the congressional committee investigating what happened about the conversation between the two.
“We know his daughter — we have firsthand testimony that his daughter Ivanka went in at least twice to ask him to ‘please stop this violence,’” congresswoman Liz Cheney said on Sunday.
“We are learning much more about what former president Trump was doing while the violent assault was underway,” Ms Cheney told ABC News’s George Stephanopoulos.
“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.
“The president could have at any moment, walked those very few steps into the [White House] briefing room, gone on live television, and told his supporters who were assaulting the Capitol to stop,” Ms Cheney said.
“He could have told them to stand down. He could have told them to go home — and he failed to do so. It’s hard to imagine a more significant and more serious dereliction of duty than that.”
The remarks by Ms Cheney came ahead of the one year anniversary of hundreds of Trump supporters storming the US Capitol with intent to overturn the results of the 2020 election.
Five people were killed after Mr Trump told his supporters to “fight like hell. And if you don’t fight like hell, you’re not going to have a country anymore”, at a rally in Washington DC.
The former president did eventually release a video message after hours of pressure.
He said to his supporters: “This was a fraudulent election, but we can’t play into the hands of these people. We have to have peace. So go home. We love you, you’re very special.”
Ms Cheney was among the members of Congress who afterwards voted to impeach Mr Trump for a second time amid accusations that he incited the violence.
On Sunday, she said the committee would start revealing more of its findings into the attack.
On Trump she added: “Any man who would provoke a violent assault on the Capitol...is clearly unfit for future office, clearly can never be anywhere near the Oval Office ever again.”
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