WASHINGTON - Last week, President Obama gave a farewell address ringing with calls to optimism, reason, and civic engagement.
The next day, President-elect Donald Trump held a raucous news conference, berating perceived enemies in the media before launching into a Twitter-fueled battle with civil rights icon John Lewis, days before Martin Luther King's Birthday.
The contrast in personal style provided a preview of the stark change coming to the Oval Office - and into American lives - after Trump's inauguration Friday.
"This is a very jarring switch we're about to go through," said Julian Zelizer, a political historian at Princeton University.
As much as any policy change, the shift in tone from Obama to Trump could be just as impactful and shape the country's dialogue and mood for the next four years, scholars say.
"It's not only their personalities - it's in many ways what they represent," Zelizer said.
Many presidents' most resonant images come not from bill signings but from indelible moments created by a confluence of history and their personal presence.
Their temperaments are often tested, and shown most clearly, amid national crisis or tragedy, or historic moments that few could foresee during an election. At these unpredictable times, their personalities guide the country and set the tone for a path forward.
"A president becomes consequential and his temperament becomes even more important at moments of great turmoil," said the renowned presidential historian Doris Kearns Goodwin.
When President Obama went to a black church after the Charleston, S.C., mass shooting and sang "Amazing Grace," he created a moment unique to his place in history.
When a Supreme Court ruling legalized same-sex marriage, Obama amplified the resonance by bathing the White House in rainbow-colored lights. Joyful crowds marked the moment there deep into the night.
Former President George W. Bush used his bravado to rally the country after 9/11, grabbing a bullhorn to give a rousing exhortation at ground zero. A former Major League Baseball owner, he defiantly took the mound in front of roaring New Yorkers weeks later to throw out the first pitch of a World Series game.
"The president is asked to be a policy leader and a symbolic leader," said Matthew Kerbel, chair of Villanova's political science department.
How might Trump, who has thrived on combat, handle a time that calls for unity?
"One of the qualities that Donald Trump actually has is in private, he's very engaging, can be a bigger-than-life figure, and what he has to do is channel that personality that got so many people excited about his election to a cause beyond a campaign - and I think he can do that," said Sen. Lindsey Graham (R., S.C.), a frequent Trump critic.
But although Twitter has helped Trump spread his message, Graham said a time of tragedy will call for more.
"What you don't want that new way of communicating to do is take away from your ability to be that reassuring figure when something really bad happens to all of us - when it's not a party thing but an American thing," he said.
Trump gets his first chance to set the tone when he stands at the Capitol on Friday for his inaugural speech.
Aides have previously said to expect a more optimistic tone, but Zelizer said the presidential transition thus far shows not to expect much change from Trump in the long term.
The months since Election Day have given every indication that he intends to govern as he campaigned: brash, unapologetic, always punching, unafraid to shatter the norms.
"That's the guy who people elected," Zelizer said.
Said Goodwin: "There's been a certain kind of grace and quiet and dignity to [Obama's] administration, and it's unpredictable what will happen with President-elect Trump."
A president's demeanor can shape not only the national tone, but his ability to rally Congress and the public.
Lyndon Johnson berated lawmakers to bend them to his will, Zelizer said. Ronald Reagan found simple clarity and spun his vision into powerful stories.
Obama offered calm amid economic panic when he was first elected.
"For some of those of us who are engaged in partisan fights, we found his equanimity to be frustrating at times, but it has had a stabilizing effect on the country," said Sen. Brian Schatz (D., Hawaii.)
On the flip side, Obama's cool, logical approach fueled critics who said he was too passive in the face of international aggression. At worst, he was branded aloof.
Trump has yet to meet a fight he can pass up. He has promised to take on corrupt elites and foreign influence and put America first.
"I alone can fix it," he thundered.
Obama campaigned with calls to hope, diversity, and unity.
"Yes we can," he declared.
Their places in American culture represent contrasting sides of the same country.
The urbane Obama played basketball with George Clooney and showcased his celebrity on cool-kid outlets such as the online comedy series Between Two Ferns.
Trump has thrived in tabloids, reality TV, and 140-character bursts on Twitter.
"The way the president embodies the office really matters to the way people think about themselves," Kerbel said.
More so than any other office, voters personally identify with their choice for president.
When the optimistic and active Franklin Delano Roosevelt, for example, took over for President Herbert Hoover, the national mood quickly lifted, even before the new president had done much, Goodwin said.
His demeanor was enough to make people feel things were going better.
That the same country has elected two drastic opposites in part reflects the times when they ran, Zelizer said.
Eight years after choosing Obama's measured mien, voters picked a man who gave voice to widespread frustration with an uneven recovery and cultural disruption.
On Friday, that voice gains new power and influence.