WASHINGTON (AP) — As newly inaugurated leaders often do, President Joe Biden began his tenure with a ritual call for American unity.

But standing on the same Capitol steps where just two weeks ago rioters laid siege to the nation's democracy, Biden's words felt less like rhetorical flourishes and more like an urgent appeal to stabilize a country reeling from a spiraling pandemic, economic uncertainty, racial tensions and a growing divide over truth versus lies.

"We must end this uncivil war," Biden declared shortly after being sworn in as the nation's 46th president.

Repairing the badly battered nation amounts to one of the greatest challenges to face an American president. The coronavirus pandemic has killed more than 400,000 Americans and is still raging out of control. The economy keeps shedding jobs, with unemployment hitting women and minorities the hardest. And the insurrection at the Capitol made clear the extent of the risks posed by the nation's deep political divisions and the embrace of conspiracies and lies by many followers of Biden's predecessor, former President Donald Trump.

"Few people in our nation's history have been more challenged or found a time more challenging or difficult than the time we are in now," Biden said.

Indeed, Biden, 78, is taking office at as grim a moment as many Americans can remember, and his inaugural celebration reflected that reality. There was no cheering crowd spread out before him on the National Mall when he took the oath of office as a consequence of the pandemic, but there were 25,000 National Guard troops securing the streets of Washington in response to the Capitol attack. Officials who did gather there wore face masks and were seated at a distance.

Trump wasn't on hand to witness the fallout of his tenure, having defied tradition and left Washington earlier Wednesday morning.

Historians have put the challenges Biden faces on par with, or even beyond, what confronted Abraham Lincoln when he was inaugurated in 1861 to lead a nation splintering into civil war or Franklin Delano Roosevelt as he was sworn in during the depths of the Great Depression in 1933.

But Lincoln and Roosevelt's presidencies are also a blueprint for the ways American leaders have turned crises into opportunities, pulling people past the partisan divisions or ideological forces that can halt progress.

"Crises present unique opportunities for large scale change in a way that an average moment might not," said Lindsay Chervinsky, a presidential historian and author of "The Cabinet: George Washington and the Creation of an American Institution." "The more intense the crisis, the more likely the country is to get behind someone to try to fix that — the concept of uniting in war or uniting against a common threat."

But by some measures, Roosevelt and Lincoln had advantages Biden does not. Roosevelt's Democratic Party had solid majorities in Congress, helping him power through his expansive agenda. Lincoln's Republican majorities were added by the secessionist push that dwindled his opponents' ranks in Congress.

Biden, meanwhile, will have the narrowest of Democratic majorities in Congress; in the 50-50 Senate, it will fall to Vice President Kamala Harris to break any ties. The Republican Party faces an existential crisis of its own making after the Trump era, and it is deeply uncertain how much cooperating with the new Democratic president fits into its leaders' plans for their future.

Still, Biden has signaled he will press Congress aggressively in his opening weeks, challenging lawmakers to pass a $1.9 trillion pandemic relief package to address the public health and economic crisis — all but daring Republicans to block him at a moment when cases and deaths across the U.S. are soaring.

Biden's ability to get that legislation passed will significantly shape both his administration's ability to tackle the pandemic and his overall standing in Washington. He's staked much of the promise of his presidency on his ability to court lawmakers from across the aisle, touting his long working relationship with Republican senators and the reputation he cultivated as a dealmaker while serving as President Barack Obama's No. 2.

But Washington has changed rapidly since then, a reality Biden's advisers insist he is clear-eyed about. Unlike Obama, he will quickly flex his executive powers on his first day in office, both to roll back Trump administration policies and to take action on the pandemic, including issuing a mask mandate on federal property. He's also pledged that his administration will vaccinate 100 million people against the coronavirus within his first 100 days in office, laying down a clear marker to judge his success or failure.

Laura Belmonte, the dean of the Virginia Tech College of Liberal Arts and Human Sciences and a professor of history, said that while Biden would be "naive" to think Washington is the same as it was when he was a senator or even when he left it as vice president, the experience he brings to the job will be invaluable in this moment.

"We don't have time for a learning curve," Belmonte said. "I cannot think of a modern president that has faced a more daunting landscape."

As he addressed the nation on Wednesday, Biden was plainspoken about the challenges ahead and the reality that his presidency will be judged on his ability to overcome them. He also nodded to some of the reasons for optimism on the horizon, including the rollout of COVID-19 vaccines and an economy poised to rebound when the pandemic ultimately passes.

But there is far less certainty about the ultimate challenge the new president faces: bridging the deep ideological, racial and factual divides that have pushed the nation to the brink.

"Unity is the path forward," he said. "We must meet this moment as the United States of America. If we do that, I guarantee you we will not fail."

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Editor's Note — Julie Pace has covered the White House and politics for The Associated Press since 2007. Follow her at http://twitter.com/jpaceDC.