And Biden charged Trump with "inciting a mob to attack the Capitol," which he said was the culmination of four years of "unrelenting attack" by the president "on the institutions of our democracy."
The president has been slammed by Democrats as well as numerous Republicans for encouraging supporters at Wednesday's rally Trump headlined near the White House to march on the Capitol to protest the joint session of Congress that was officially certifying Biden’s Electoral College victory over the president.
Trump supporters breached security at the Capitol, entering and vandalizing parts of the building, triggering a lockdown and forcing lawmakers in the House and Senate to suspend their sessions for roughly six hours. Biden described the attack as one of the "darkest days in the history of our nation."
Biden, speaking in his hometown of Wilmington, Del., as he introduced federal appeals court judge Merrick Garland as the nominee for attorney general, lamented that "I wish we could say we couldn’t see it coming. But that wasn’t true. We could see it coming."
The president-elect argued that the "past four years we’ve had a president who’s made his contempt of our democracy, our Constitution, the rule of law, clear, in everything he has done. He unleashed an all-out assault on the institutions of our democracy from the outset. And yesterday was but the culmination of that unrelenting attack."
Biden emphasized that "what we witnessed yesterday was not dissent, it was not disorder, it was not protest. It was chaos. They weren’t protesters. Don’t dare call them protesters. They were a riotous mob. Insurrectionists. Domestic terrorists. It’s that simple."
Biden accused Trump of "inciting a mob to attack the Capitol, to threaten elected representatives of the people of this nation and even the vice president, to stop the Congress from ratifying the will of the American people in a just-completed, free and fair election. Trying to use a mob the silence the voices of nearly 160 million Americans who summoned the courage in the face of a pandemic that threatened our health our lives to cast that sacred ballot."
Biden, in his speech, said that during the storming of the Capitol his granddaughter texted him a photo of police in full military gear lining the steps of the Lincoln Memorial during a Black Lives Matter protest last year.
"No one can tell me that if it had been a group of Black Lives Matter protesting yesterday there wouldn't — they wouldn't have been treated very, very differently than the mob of thugs that stormed the Capitol," Biden emphasized. And he stressed that "we all know that is true, and it is unacceptable. Totally unacceptable."
The president-elect spoke soon after Senate Democratic Leader Chuck Schumer urged that Vice President Pence should "immediately" invoke the 25th Amendment and remove Trump from office. And Schumer warned that if Pence refuses, Congress should "impeach the president."
"What happened at the U.S. Capitol yesterday was an insurrection against the United States, incited by the president," the longtime senator from New York wrote in a statement. "This president should not hold office one day longer."
"The quickest and most effective way – it can be done today – to remove this president from office would be for the vice president to immediately invoke the 25th Amendment," Schumer emphasized. "If the vice president and the Cabinet refuse to stand up, Congress should reconvene to impeach the president."
House Speaker Nancy Pelosi echoed Schumer’s comments a few hours later.
But Biden declined to discuss the comments made by the top two Democrats in Congress.
"I’m not going to speak to that today," Biden told reporters at the top of his speech.
Biden transition spokesperson Andrew Bates said later in a statement that "President-elect Biden and Vice President-elect Harris are focused on their duty -- preparing to take office on Jan. 20 -- and will leave it to Vice President Pence, the Cabinet and the Congress to act as they see fit."
The 25th Amendment to the Constitution includes a section allowing the vice president and a majority of Cabinet members to declare a president "unable" to perform the job.
Fox News' Jacqui Heinrich, Peter Doocy, and Patrick Ward contributed to this report