NEW YORK (AP) — When Joe Biden addresses the country for the first time as president, his inaugural speech is likely to echo calls for unity that predecessors have invoked since the first time George Washington was sworn in.

Unity has since been a theme, and an anxiety, for many incoming presidents, who have faced economic and social crises and moments when the very future of the U.S. was in doubt. Historians mention the first inaugural speeches of Thomas Jefferson and Abraham Lincoln as possible parallels for Biden, who has said his goal is to “restore the soul” of the country.

Biden, who assumes office just two weeks after an armed seige of the U.S. Capitol by supporters of President Donald Trump, will preside over a nation in which millions believe Trump's baseless claims that the election was stolen. Few presidents have faced such questions about their own legitimacy.

“Unity has always been an aspiration," says presidential historian Douglas Brinkley. “It seems like whenever we have foreign policy flare-ups, we use the word freedom. But when we have domestic turmoil we use the word unity.”

The United States was forged through compromise among factions that disagreed profoundly on slavery, regional influence and the relative powers of state and federal government. When Washington assumed office in 1789 he cited the blessings of providence in noting that “the tranquil deliberations and voluntary consent of so many distinct communities, from which the event has resulted, cannot be compared with the means by which most governments have been established.”

Jefferson was the third U.S. president, and the first whose rise was regarded by opponents as a kind of emergency. The 1800 election won by Jefferson marked the beginning of competing political parties — Jefferson was a leader of the Democratic-Republican Party, losing incumbent John Adams a Federalist — and critics regarded the new president as a dangerous atheist. "JEFFERSON — AND NO GOD!!!” was how one Federalist paper described Jefferson's candidacy. Adams did not attend the inauguration, a breach rarely repeated although Trump has vowed to do the same.

“Let us then, fellow citizens, unite with one heart and one mind," Jefferson urged in his address. "We are all republicans: we are all federalists. If there be any among us who would wish to dissolve this union, or to change its republican form, let them stand undisturbed as monuments of the safety with which error of opinion may be tolerated, where reason is left free to combat it."

Supreme Court Chief Justice John Marshall, a Federalist who administered the oath of office to Jefferson, wrote later that the speech was “in the general well judged and conciliatory.”

Lincoln's pleas were more dire, and tragically unmet, despite what historian Ted Widmer calls his “genius to combine urgency with literary grace.” Seven out of 11 future Confederate states had seceded from the U.S. before he spoke, in March 1861, over fears he would end slavery. The Civil War would begin a month later. “We are not enemies, but friends,” Lincoln had insisted, reminding fellow Americans of their “mystic chords of memory” while also warning that resistance to the will of voters would destroy democracy.

"A majority held in restraint by constitutional checks and limitations, and always changing easily with deliberate changes of popular opinions and sentiments, is the only true sovereign of a free people. Whoever rejects it does of necessity fly to anarchy or to despotism,” he said.

Historian David Greenberg, whose books include “Nixon's Shadow" and “Republic of Spin,” cites Richard Nixon's inaugural in 1969 as another speech given at a time of social turmoil. The U.S. was violently divided over the Vietnam War and civil rights, and Nixon himself had long been seen as an unprincipled politician exploiting fears and resentments — appealing to what he would call “the silent majority.” His speech at times was openly and awkwardly modeled on the 1961 inaugural of John F. Kennedy, who had defeated Nixon in 1960.

“We are caught in war, wanting peace. We are torn by division, wanting unity,” Nixon stated. “We cannot learn from one another until we stop shouting at one another — until we speak quietly enough so that our words can be heard as well as our voices.”

Some presidents asked for unity, others asserted it.

Franklin Roosevelt, elected in a landslide in 1932 during the Great Depression, said in his first inaugural speech: “If I read the temper of our people correctly, we now realize as we have never realized before our interdependence on each other.” Four years later, having won by an even greater landslide, he declared the country had “recognized” a need beyond financial help, a “deeper” need, “to find through government the instrument of our united purpose.”

Unity can prove more imagined than real. When James Buchanan spoke in 1857, three years before the Civil War, he claimed that “all agree that under the Constitution slavery in the states is beyond the reach of any human power except that of the respective states themselves wherein it exists.” Rutherford B. Hayes, whose presidency was marked by the retrenchment of federal troops from the post-Civil War South and ongoing resistance from Southern whites to equal rights for Blacks, declared during his 1877 inaugural that true peace could be achieved through the “united and harmonious efforts of both races” and the honest work of local self-government.

“A president often claims the country is ‘united’ behind a belief when it’s more wishful thinking than reality,” Widmer says. “I’m not sure how many Americans wanted to do something for their country after JFK asked them to — although there were impressive new kinds of volunteers, like the Peace Corps. And I think that many Americans still appreciated help from the government, even after Ronald Reagan declared that ‘government is the problem.’ That’s the problem with soundbites: They often oversimplify.”