WASHINGTON — President-elect Joseph R. Biden Jr. denounced the storming of the Capitol on Wednesday as the violent expression of President Trump’s refusal to accept his defeat, calling it “an assault on the citadel of liberty” and saying the president had stoked the mob with his brazen and false claims that the 2020 election had been stolen.
In direct, forceful language, Mr. Biden called the scenes of chaos in the halls of Congress “a dark moment” in the nation’s history, appealed for calm and made clear that he held Mr. Trump accountable for instigating violence that left members of both parties and allies around the world appalled.
“At their best, the words of a president can inspire. At their worst, they can incite,” Mr. Biden said.
“This is not dissent,” the president-elect said in remarks from Delaware as scenes of the armed takeover of the Capitol played out on television screens. “It’s disorder. It’s chaos. It borders on sedition and it must end now.”
The day had started as one of triumph for Mr. Biden and his party, with Democrats coming off elections the day before that sealed control of the Senate by picking up two seats in Georgia and Congress scheduled to clear away the last formal Republican objections to his victory by certifying the Electoral College outcome.
Filling out his cabinet, Mr. Biden chose Judge Merrick B. Garland, whose Supreme Court nomination Republicans blocked in 2016, to be attorney general, placing the task of repairing a beleaguered Justice Department in the hands of a centrist judge. The choice left some Democrats on the left of the party disappointed that he had not picked a woman or person of color and underscored Mr. Biden’s willingness to seek bipartisan consensus.
But by early afternoon, the day had devolved into an intensely jarring reminder of what Mr. Biden will face when he takes office on Jan. 20: He will not only inherit a country racked by a pandemic and economic crisis, but also a political fabric that has been ripped apart by Mr. Trump and will not easily be woven back together.
The assault on the Capitol by pro-Trump demonstrators devolved into a physical confrontation that halted the process of certifying the Electoral College outcome and was egged on by an incumbent president who on Wednesday morning raged to thousands of his supporters that the election was “rigged” and vowed, “We will never concede.”
With Mr. Trump remaining mostly silent immediately after the mob entered the Capitol, Mr. Biden called on the president to “go on national television now to fulfill his oath and defend the Constitution and demand an end to this siege.”
“To storm the Capitol,” he continued. “To smash windows, occupy offices. The floor of the United States Senate, rummaging through desks. On the Capitol, on the House of Representatives, threatening the safety of duly elected officials. It’s not protest. It’s insurrection.”
Shortly after, Mr. Trump posted on Twitter a one-minute video in which he empathized with the rioters because “we had an election that was stolen from us,” but then urged them to “go home now. We have to have peace. We have to have law and order.”
The effect of the day’s events on Mr. Biden’s political strength remained unclear. In one sense, they were a reminder that in the view of Mr. Trump’s most die-hard supporters his election was illegitimate, a belief that could inhibit some Republicans in a closely divided Congress from working with him.
Or the “God-awful display” at the Capitol, as he put it, might push the parties together in some sort of temporary solidarity that could give him a chance to forge some early bipartisan deals.
Mr. Biden expressed hope that it would be the latter.
“The work of the moment and the work of the next four years must be the restoration of democracy, of decency, honor, respect, the rule of law,” he said, adding later: “We must step up.”
It was a reminder, if Mr. Biden or any of his aides needed one, that little in his transition to the presidency was normal.
As the rioters stormed the Capitol, Mr. Biden set aside plans to deliver a speech on the economy, in which he had been expected to hail the Georgia victories and to emphasize several of his economic priorities, including reiterating calls for another round of financial aid to help people, businesses and state and local governments weather economic pain from the virus.
Mr. Biden’s advisers are deep into the process of developing policy proposals to deliver to Congress in the coming weeks, starting with another stimulus package. Senator Chuck Schumer of New York, who will be the Democratic majority leader after Mr. Biden is inaugurated, told reporters Wednesday morning that lawmakers’ first priority will be approving the $2,000 payments to individuals that Mr. Biden and the two victorious Senate candidates, Jon Ossoff and Raphael Warnock, promised voters they would deliver if Democrats won both elections.
The Biden team is also drafting proposals to implement the president-elect’s “Build Back Better” campaign agenda, including new government spending on clean energy, infrastructure, health care and education, financed by tax increases on the rich and corporations.
The Democratic victories in Georgia put Mr. Biden’s party in control at both ends of Pennsylvania Avenue and reduced the risk of total partisan gridlock in Congress, at least for two years.
Without Senator Mitch McConnell, Republican of Kentucky, as the iron-fisted leader of the Senate, Mr. Biden’s campaign promise of a return to bipartisanship will be put to the test. Now, Mr. Schumer and Mr. Biden’s allies will bring the new president’s proposals to the Senate floor for a vote. And even with just the narrowest of margins — a 50-to-50 split that can be broken by Vice President-elect Kamala Harris — he may be able to turn some of those proposals into law.
“McConnell would have been a recipe for total stasis, total gridlock,” said Matt Bennett, a veteran Democratic strategist at Third Way, a moderate think tank. “With Schumer in control of the calendar, he’s got the opportunity to do some really substantial things.”
Liberal groups that supported Mr. Biden expressed hope on Wednesday that the Georgia wins would allow him to push an ambitious and expensive agenda that addressed the current economic crisis and long-running inequalities in the American economy.
Mr. Biden and the Democratic majority will take office with a mandate for “a significant down payment on creating an economy that works for all Americans,” said Frank Clemente, the executive director of Americans for Tax Fairness, which has pushed Mr. Biden to enact substantial tax increases on the wealthy. “That is in the neighborhood of $3 to $4 trillion over 10 years, which is paid for by making the rich and corporations pay their fair share in taxes.”
Other interest groups quickly seized on the Georgia results to ratchet up the pressure on Mr. Biden to make good on his campaign promises.
“We are fighting to defund ICE and C.B.P., to hold these agencies accountable for the pain and deaths of immigrants they’ve caused, and for citizenship for the 11 million undocumented people living in the U.S.,” said Greisa Martinez Rosas, the executive director of United We Dream, a progressive advocacy group, referring to federal immigration agencies.
Mr. Biden’s allies in the Senate expressed optimism that, armed with committee chairmanships and control of the legislative calendar, they could advance the president-elect’s policy goals.
“We need to fix a lot of the damage Trump’s done, and then there’s pent-up demand for a whole lot of things — what do we do about climate and about racial inequality, about wealth inequality, about structural racism,” said Senator Sherrod Brown of Ohio, who is set to be the top Democrat on the Senate Banking Committee.
Senator Thomas R. Carper, Democrat of Delaware, told reporters on Capitol Hill that “there’s a bipartisan agenda there that can unite us, and it should.”
“There’s a hunger for rebuilding our roads, highways, bridges and transit systems,” he said. “There’s a hunger for rebuilding our wastewater, clean drinking water infrastructure.”
Mr. Biden has also proposed the most ambitious climate agenda of any president in history, including $2 trillion in spending on green initiatives. A majority in the Senate gives Mr. Biden options to make some of that happen.
Democrats are now expected to use a first-out-of-the-gate coronavirus economic stimulus package as a vehicle for hundreds of billions of dollars in spending to aid the renewable energy economy, just as Mr. Obama used a 2009 economic stimulus law to push through $90 billion in green energy spending.
Senate Democrats are expected to continue to look for ways to weave climate provisions into other major legislation, such as military, farm and labor bills. And Mr. Schumer also promises to get creative: For example, he plans to use a budgetary procedure, called reconciliation, that can skirt a filibuster to muscle through climate spending and tax policy.
But Mr. Biden’s agenda will be constrained by the Democrats’ narrow advantages in the House and in the Senate, where moderate Democrats such as Senator Joe Manchin III of West Virginia and Senator Kyrsten Sinema will wield vast power over which plans can pass.
“The name of the game is still going to have to be modest, incremental progress on a bipartisan basis,” said Michael Steel, a partner at Hamilton Place Strategies in Washington who was a top aide to Representative John A. Boehner when the Ohio Republican was House speaker. “I can’t come up with a universe in which they are not better off doing a bipartisan process and a bipartisan product. I know that will annoy the left to no end, but that’s the way this president can get results.”
Before the outbreak of violence on Capitol Hill, Mr. Biden signaled on Wednesday morning that despite the shift of Senate control to Democrats, he would still attempt to build legislative coalitions with Republicans on his top priorities — many of which would require 60 votes to clear a Senate filibuster.
“Georgia’s voters delivered a resounding message yesterday: They want action on the crises we face and they want it right now,” Mr. Biden said in a written statement. “On Covid-19, on economic relief, on climate, on racial justice, on voting rights and so much more. They want us to move, but move together.”
Privately, some Republicans with long histories on Capitol Hill said Wednesday that the storming of the House and Senate could shock some Republican senators — the group who had pushed back against their fellow Republicans’ attempts to overturn Mr. Biden’s election and install Mr. Trump for a second term — into a greater willingness to partner with Mr. Biden on policy issues.
A high-profile business lobbying group that has long supported many Republicans, the National Association of Manufacturers, denounced Mr. Trump on Wednesday for inciting the violence and suggested it was time for his administration to invoke a constitutional provision to remove him.
Vice President Mike Pence “should seriously consider working with the cabinet to invoke the 25th Amendment to preserve democracy,” the group’s president, Jay Timmons, wrote in a news release.
Emily Cochrane, Nicholas Fandos and Coral Davenport contributed reporting