WASHINGTON — President Biden forcefully denounced former President Donald J. Trump for promoting lies and tearing down democracy because he could not stand the fact that he lost a free and fair election, accusing his predecessor and his allies of holding “a dagger at the throat of America.”
In his most sustained and scathing attack on the former president since taking office, Mr. Biden used the anniversary of the Jan. 6 mob assault on the Capitol to condemn Mr. Trump for waging an “undemocratic” and “un-American” campaign against the legitimacy of the election system that he likened to the actions of autocrats and dictators in faraway countries.
“The former president of the United States of America has created and spread a web of lies about the 2020 election,” Mr. Biden said, standing in the same National Statuary Hall invaded by throngs of Trump supporters a year ago. “He’s done so because he values power over principle, because he sees his own interests as more important than his country’s interests and America’s interests, and because his bruised ego matters more to him than our democracy or our Constitution. He can’t accept he lost.”
Without using Mr. Trump’s name, the president assailed the “defeated former president” for trying to rewrite history and for casting the attackers of a year ago as patriots. “Is that what you thought when you looked at the mob ransacking the Capitol, destroying property, literally defecating in the hallways, rifling through desks of senators and representatives, hunting down members of Congress?” Mr. Biden asked. “Patriots? Not in my view.”
“Those who stormed this Capitol and those who instigated and incited and those who called on them to do so,” he added, “held a dagger at the throat of America, at American democracy.”
Mr. Trump fired back moments later with the first of a string of written statements issued from his Mar-a-Lago estate in Florida. “This political theater is all just a distraction for the fact Biden has completely and totally failed,” Mr. Trump wrote. “The Democrats want to own this day of January 6th so they can stoke fears and divide America,” he added. “I say, let them have it because America sees through theirs [sic] lies and polarizations.”
Mr. Biden’s speech kicked off a commemoration that, instead of showcasing American unity, underscored just how fractured the nation remains a year after Mr. Trump’s refusal to accept defeat at the ballot box stirred backers to invade the Capitol, disrupt the counting of the Electoral College votes and send lawmakers scurrying for safety.
Mr. Biden and Democratic leaders scripted a day of addresses, discussions and a candlelight vigil while Republican leaders stayed away, with many G.O.P. senators heading to Georgia for the funeral of their former colleague, Johnny Isakson.
In the House chamber, the only Republican member spotted on the floor for a moment of silence marking the anniversary was Representative Liz Cheney of Wyoming, one of the party’s leading critics of Mr. Trump. She was joined in the front row by her father, former Vice President Dick Cheney, himself a former member of the House.
Once the bête noire of the left, Mr. Cheney was greeted cordially by Speaker Nancy Pelosi and other Democrats, who have praised his daughter for her courage, an extraordinary spectacle reflecting how much Mr. Trump has transformed the political dynamics of the country.
“I’m deeply disappointed we don’t have better leadership in the Republican Party to restore the Constitution,” Mr. Cheney told Jonathan Karl of ABC News.
Earlier in the morning, his daughter castigated fellow Republicans for “looking the other way” rather than confront the serious threat represented by the Capitol attack.
“All of my colleagues, anyone who attempts to minimize what happened, anyone who denies the truth of what happened, they ought to be ashamed of themselves,” Ms. Cheney said on the “Today” show on NBC. “History is watching, and history will judge them.”
Over in the Senate chamber, not a single Republican senator showed up as Democrats took to the floor after Mr. Biden’s speech to continue assailing Mr. Trump, “the worst president in modern times,” as Senator Chuck Schumer of New York, the Democratic majority leader, put it.
“It was Donald Trump’s big lie that soaked our political landscape in kerosene,” Mr. Schumer said. “It was Donald Trump’s rally on the Mall that struck the match. And then came the fire.”
To emphasize the significance of the event, Ms. Pelosi sponsored an afternoon discussion led by Carla Hayden, the librarian of Congress, with the historians Doris Kearns Goodwin and Jon Meacham, who talked about other moments of peril like the tumultuous years leading up to the Civil War. The panel was introduced with a video specially produced by the cast of “Hamilton” performing a song from the hit musical about the founding of the country.
The disparate approaches to the anniversary reflected how much Jan. 6 has become interpreted through a political lens. Democrats view the storming of the Capitol as an existential threat to constitutional democracy unlike any in modern times. Most Republicans would rather focus on anything else, with some convinced that it is being used as a partisan weapon against them and others fearful of crossing Mr. Trump, who continues to wield outsize power within the party.
Feelings remain raw on Capitol Hill, a place of post-traumatic stress that has yet to fully recover from the psychological and political scars of an assault that led to at least seven deaths as well as injuries to 150 police officers. More than the usual acrimony over legislative differences, the legacy of Jan. 6 has exacerbated the toxic rift between members and staff aides on opposite sides of the aisle.
While Mr. Biden had hesitated to engage in a back-and-forth with his predecessor, he used his 20-minute speech to more directly blame Mr. Trump than ever before for encouraging the violence a year ago and then sitting in his private White House dining room watching television and “doing nothing for hours as police were assaulted, lives were at risk, and the nation’s capital under siege.”
He offered his most extended rebuttal of the false claims that the 2020 election was somehow stolen, noting that repeated recounts, court battles and inquiries had turned up no meaningful fraud. He pointed out that Republicans did not challenge Republican victories for Congress and governor’s mansions based on the same balloting they claim was illegitimate in the presidential race.
Mr. Biden took on efforts to recast the narrative of what happened on Jan. 6, which some Republicans have dismissed as little more than a protest that got out of hand. “This wasn’t a group of tourists,” Mr. Biden said. “This was an armed insurrection. They weren’t looking to uphold the will of the people. They were looking to deny the will of the people.”
Mr. Biden also touched on voting rights legislation stalled in the Senate, although he has a separate speech on the subject scheduled for next week. Vice President Kamala D. Harris, who spoke before Mr. Biden, said, “We must pass voting rights bills that are now before the Senate.”
Republicans accused the White House and Democrats of politicizing the attack to promote legislation meant to benefit their own party and rejected Mr. Biden’s indictment of Mr. Trump. “What brazen politicization of January 6 by President Biden,” Senator Lindsey O. Graham of South Carolina wrote on Twitter following the speech.
Mr. Graham himself broke with Mr. Trump on that day a year ago, saying, “All I can say is count me out, enough is enough.” But it did not take long for him, like most Republicans, to fall in line behind the former president again.
In a series of tweets on Thursday, Mr. Graham denounced the violence of a year ago but not Mr. Trump. “President Biden and Vice President Harris’s speeches today,” he wrote, “were an effort to resurrect a failed presidency more than marking the anniversary of a dark day in American history.”
Other Republican allies of the former president used the occasion to spread unfounded conspiracy theories. Representatives Matt Gaetz of Florida and Marjorie Taylor Greene of Georgia appeared on a podcast hosted by Stephen K. Bannon, a former chief strategist for Mr. Trump, trying to pin blame for the riot on Democrats or federal authorities.
“We’re here to get to the truth behind Jan. 6, the federal government’s own involvement with it,” Mr. Gaetz said.
They later held a news conference in an office building near the Capitol, again promoting unproven conspiracy theories and decrying the treatment of those charged with crimes related to the attack.