A man convicted of dozens of felonies versus a criminal prosecutor. An architect of abortion bans versus a champion of reproductive freedom. An elderly white man fixated on the past versus a mixed-race daughter of immigrants leaning into the future.

One hundred days from the US presidential election, the choice for voters has never been so clear cut. Kamala Harris, 59, the de facto Democratic nominee after the dramatic withdrawal of Joe Biden, is a progressive person of colour bidding to become the first female president in America’s 248-year history.

Donald Trump, at 78 the oldest nominee in history, is a populist-nationalist who has demonised immigrants, gained backing from far-right extremists and tapped into white Christian nostalgia by promising to “make America great again”.

“In this moment, I believe we face a choice between two different visions for our nation, one focused on the future, the other focused on the past,” Harris told members of the historically Black sorority Zeta Phi Beta in Indianapolis on Wednesday. “And with your support, I am fighting for our nation’s future.”

Biden has previously spoken of a “battle for the soul of the nation” and Trump has described this election as “the final battle”. But the nomination of Harris will be clarifying about the culmination of a tumultuous decade and a collision of two Americas: one liberal, diverse and optimistic, the other conservative, nativist and, in Trump’s telling, driven by grievance and vengeance.

Halifu Osumare, professor emerita in the department of African American and African studies at the University of California, Davis, said: “The difference between the candidates couldn’t be any starker. To me it represents this country and its schizophrenia. This country is both racist to its core yet the leader of the world in the rights of the individual and democracy.

“This election is going to play out that schizophrenia because you’ve got a good deal of the nation who wants to take us back to those days where white supremacy was absolutely dominant, and those who want us to evolve as a human species. We need somebody who has humanity at her core in order to do that.”

The road that led here began with the election of Barack Obama, America’s first Black president, in 2008. For millions of Americans, Obama represented hope; for millions of other Americans, he represented fear that the country they grew up in was disappearing. Whereas white Christians made up 54% of the US population in 2008, they have now slipped into the minority and make up only 44%.

Racially motivated backlash against Obama was evident in the stirrings of the populist Tea Party movement. Then came Trump’s entry into politics as a “birther”, questioning whether Obama had in fact been born in Kenya and was therefore ineligible for the presidency.

Again, Trump offered hope to one America and fear to the other. He embodied a rage against change, political correctness and liberal elites, gaining traction in small towns and rural areas that felt left behind. He scapegoated immigrants as the source of blame, creating an us-versus-them dynamic, and promised to build a border wall to keep them out.

The country faced a clear choice in 2016 and handed Trump victory over Hillary Clinton in the electoral college, though there were complicating variables such as her status as a former first lady and the FBI reopening an investigation into her handling of classified information.

Four years and one global pandemic later, Trump, a white man who was the oldest president ever, was defeated by Joe Biden, a white man who was even older and a moderate who won back white working-class votes that Clinton had lost in the rust belt. In 2024, the world was braced, somewhat wearily, for a rematch.

Moe Vela, a former senior adviser to Biden when he was vice-president, said: “When it was Biden and Trump, you had two septuagenarians that created a battle of senior citizens. Now you have not only gender, not only the past versus the future, not only a difference in heritage – you have also the stark contrast in hope versus hate.”

In the past month, American politics has moved at incredible speed, upending all certainties. Biden flopped at a presidential debate in Atlanta, Trump survived an assassination attempt at a campaign rally in Pennsylvania and, as a chorus of Democrats questioned his age and mental acuity, Biden became the first incumbent since 1968 to announce he would not seek re-election.

The party quickly rallied around Harris, a former US senator, prosecutor and California attorney general, with an avalanche of endorsements, fundraising and memes. She hit the campaign trail with electrifying speeches and Beyoncé tracks, providing a shot of adrenaline that flipped Democrats from doom and gloom to giddy optimism. Opinion polls show Harris outperforming Biden among Black, Latino and young voters, and running more or less even with Trump.

Leon Panetta, a former defence secretary and CIA director, said: “There’s a hundred days to go to the election and, in a year where everything has pretty much happened, it’s hard to tell how this all plays out. But I don’t think there’s any question that the Democrats are very much back in this race and are looking a hell of a lot better than they did a few weeks ago.”

Panetta, who served in various capacities under nine US presidents, has witnessed growing polarisation and a coarsening of political discourse. “It’s obvious that America in these last number of years has become more divided, more partisan, and our democracy in many ways has become much more dysfunctional as a result of those divisions,” he added. “Kamala Harris presents a message that we could have a better America in the future, and we need that message of hope.

“The message of Trump, whether he wanted to change it or not, still gets trapped by his own sense of retribution, vengeance and going after people. That’s not what Kamala Harris is about and so the American people are going to have a real choice here in November to decide what kind of direction we want for our country. The more defined that difference is, the better the chances are that the Democrats can win.”

Born in Oakland, California, to an Indian mother and a Jamaican father, Harris is the anti-Trump in myriad ways. She is 19 years younger, instantly neutralising the age argument and turning it against her opponent, whose ramblings and name confusions will be under special scrutiny.

She has been the face of the Biden campaign on the issue of abortion as reproductive rights became an animating issue after the supreme court in 2022 overturned the landmark 1973 Roe v Wade decision. She is expected to stick largely to Biden’s foreign policy playbook on Ukraine, China and Iran but could strike a tougher tone with Israel over the war in Gaza.

Her sudden ascent punctured Republican balloons after a successful party convention in Milwaukee, where Trump was almost deified after his defiant response – “Fight! Fight! Fight” – to a near-death experience. His entrance to the sound of It’s a Man’s Man’s Man’s World, and speeches by the likes of wrestler Hulk Hogan, underlined an image of old-school machismo.

The Trump campaign, which relished a contest with the ailing Biden, is now having to rapidly adapt to the new challenge of Harris. It has begun casting her as a leftwing radical from California who was the “co-pilot” of what they say are the Biden administration’s failed policies on immigration and inflation.

Trump told a rally in Charlotte, North Carolina, this week: “For three and a half years, Lyin’ Kamala Harris has been the ultra-liberal driving force behind every single Biden catastrophe … As border czar, Kamala threw open our borders and allowed 20 million illegal aliens to stampede into our country from all over the world.”

Republican representative and rightwing media have mispronounced her name, mocked her laugh (“Cackling Kamala”), and invoked diversity, equity and inclusion programmes to brand her potentially the “first DEI president”. Commentators predict a torrent of bigotry, racism and misogyny reminiscent of the playbooks deployed against Obama and Clinton. The tone of the two campaigns could not be more different.

Tara Setmayer, co-founder and chief executive of the Seneca Project, a women-led Super Pac, said: “That’s the decision. It’s between democracy versus autocracy, and progression versus regression. Usually a future-forward vision wins out. But we’ll see. It’s going to be a hell of a battle. When you think we were battling for the soul of America in 2020, this is the battle for the soul of America on steroids.”

The clarity of the choice raises the temperature in an already febrile atmosphere. The attempt on Trump’s life came after years of political violence that included the shooting of representative Steve Scalise, a hammer attack on former House speaker Nancy Pelosi’s husband and the January 6 riot at the US Capitol.

Both parties now head into an “Armageddon election” in which they say the American way of life is on the line. Winning will signify total vindication; losing will signify total catastrophe. How would Trump’s fervent base react to defeat by a Black woman? At a rally for Trump’s running mate, JD Vance, in Middletown, Ohio, this week, state senator George Lang warned: “I’m afraid if we lose this one, it’s going to take a civil war to save the country, and it will be saved.”

Differences personified by Harris and Trump appear irreconcilable. David Blight, a professor of American history at Yale University, said: “It’s about crushing the other side. There’s no bipartisanship about this election except for the ‘never Trumpers’ [traditional Republicans who oppose Trump], who have seen a light and don’t want to live in a country with that kind of authoritarianism.

“We’re on the brink of something here.”