Somewhere between President Biden’s decision to drop out of the presidential race last month and Barack and Michelle Obama’s rousing set of speeches at the Democratic National Convention on Tuesday night, the incumbent Democratic Party decided it was the party of “hope” again.

While Vice President Kamala Harris and other Democrats will fight for a “hopeful, forward-looking America,” her opponent, former President Trump, “wants us to think that this country is hopelessly divided,” said former President Obama.

“Hope,” his wife said, “is making a comeback!”

It is a familiar mantra for the Obamas, and one that has worked for their party before. President Obama wrote a book called “The Audacity of Hope,” and he ran and won on the concept in 2008 — with posters of his face in bold colors above the letters H-O-P-E seeming ubiquitous that political cycle.

But Obama was running against an incumbent Republican Party that had just had eight years in power under President George W. Bush. He was running not just on “hope,” but as “change” — which felt like a natural pairing.

For a party already in power, as the Democrats are now, “hope” is perhaps a less expected, more unique and in some ways far more audacious rallying cry. It can’t be a repudiation of where the country is currently headed, only of where it once was headed — and where it could be headed again.

It also makes “perfect sense” in this political moment, said Bob Shrum, director of the Center for the Political Future at USC.

Democrats are pushing an incredibly clear, two-part message, Shrum said. The first part is that “Trump is bad,” which he has made easy for his opponents to argue “because of the stuff he goes out and says,” Shrum said. “Every day he proves he is bad.”

The second part of the message is that “there is a new way forward” with Harris, Shrum said — and she and her surrogates, including the Obamas, have been selling that part just as well.

Of course, Democrats claiming the mantle of “hope” is possible only because of several unique circumstances.

It is possible because an older, less inspiring, sitting one-term president was swapped out at the last minute for his much younger vice president, whose victory would shatter one of the nation’s oldest and most enduring glass ceilings by putting a woman of color in its highest office for the first time.

Hope as a concept would not have worked for Biden, whose age and mental acuity were in question and who seemed to be tottering toward the election with little wind in his political sails. Hope would have seemed absurd as a Biden slogan, not just because of his incumbency but because of his decades-long membership in the old guard of American politics.

It is also possible because Harris is running against Trump, a former one-term president himself whose bid for a second term — which beat out those of fresher Republican faces — promises a return to a previous chapter more than the start of a promising new one.

A scene Tuesday night at the Democratic National Convention.

(Robert Gauthier/Los Angeles Times)

For Harris, a message of “hope” seems a natural political fit just as it did for Obama, Shrum said — and not least because it has been buzzing on the lips of many Democrats since Biden stepped aside. Like Obama and unlike Biden, Harris can run not just on hope, he said, but also as change.

“She is change compared to Donald Trump,” Shrum said. “She is change by virtue of her persona, she’s change by virtue of her personality and the way she comes across to people. And I think it’s flummoxed the Trump people. They don’t know where to go.”

Loren Goldman, an associate professor of political science at the University of Pennsylvania, has studied the use of hope as a political tool through history. He said he was not surprised Democrats are “embracing the language of hope.”

It allows them to “claim the mantle of the future” after being bogged down by concerns about Biden’s age, let’s them position Harris as an inheritor of Obama’s legacy, and contrasts her well with Trump, whose “invocation of American carnage strikingly rejected hope.”

Democrats know that many in their base went from fearing a devastating loss under Biden to hoping for a hard-fought win with Harris. Michelle Obama tapped directly into that feeling, acknowledging its newness and contrasting it with her own recent, pre-Harris fears.

“To be honest, I am realizing that until recently, I have mourned the dimming of that hope — and maybe you’ve experienced the same feelings,” she said. “That deep pit in my stomach, a palpable sense of dread about the future.”

But now, Obama said, Americans of all political persuasions have the opportunity to be “the anecdote to the darkness and division” they see, namely by marrying “hope” with “action” and voting for Harris.

They can “stand up for what we know in our hearts is right,” she said, “not just for our basic freedoms, but for decency and humanity, for basic respect, dignity and empathy, for the values at the very foundation of this democracy.”

Former President Obama hammered the same ideas. He said Harris represented hope for a better future — and Trump a replay of the past.

“We have all seen that movie before,” he said of Trump. “And we all know that the sequel is usually worse!”

America is “ready for a new chapter” and “ready for a better story,” Obama said.

The message clearly resonated with many of the party loyalists in the audience, who gave both Obamas massive ovations. More than a few cried openly on the convention floor.

Political experts say both hope and fear can be major political motivators. While the Republicans have gone for the latter, with much of their own convention focused on the threat of undocumented immigrants and dangerous criminals, Democrats are making a clear play for the former.

Whether that gambit will resonate enough among average American voters — especially those concerned about the current state of the country, who are struggling with inflation or worried about immigration or foreign policy under Biden, whose record Harris can’t entirely run away from — is yet to be seen.

Hope can be a hard thing to harness. But there are signs it’s working.

In February, a New York Times/Siena poll found that just 10% of Biden voters said they were happy, excited or hopeful about the election, compared with 20% of Trump voters. The same poll last month found 21% of Harris voters felt that way, compared with 29% of Trump voters.

Young voters can be especially motivated by hope, Shrum said — and their support for Harris is much higher than it was for Biden. A Times/Siena poll in June showed Biden leading Trump by 6 percentage points among registered voters younger than 30 nationally. Late last month, the same poll showed Harris leading Trump among the same voters by 18 points.

Shrum said that shift is important. “They are going to turn out,” he said. “The enthusiasm is way up.”

Mark DiCamillo, a political pollster for decades and director of the UC Berkeley Institute of Governmental Studies poll, said being the “candidate of hope and optimism is, generally speaking, a good thing” in American politics.

Still, he said, presidential votes are also hugely personal decisions for many Americans — decisions they make based on personality — and many still don’t feel like they know Harris. Her job during her scheduled DNC speech Thursday, he said, is to change that — to show she doesn’t just represent hope, but can inspire it.

“She needs to get people comfortable with her. Will she command authority? Project strength on the world stage?” DiCamillo said. “There’s lots of things that she needs to do to reinforce her image with voters and show she is up to the task.”