WASHINGTON (AFP) - The protagonists are set: Hillary Clinton versus Donald Trump. The battleground? Fifty states. Voters are set for a historic, bruising spectacle as two of America's most polarising figures wage war for the White House.
On the Democratic side is a candidate with more than three decades of political experience, a pioneering if controversial stateswoman determined to shatter the ultimate glass ceiling and become the nation's first woman commander-in-chief.
The Republican standing in her way is the brash billionaire and political neophyte who rewrote the campaign playbook as he vanquished his many rivals for the nomination with a mudslinging unparalleled in modern American politics.
The ferocity of the primaries - few people around the world have seen a modern US presidential race characterised by such insulting and denigrating attacks - promises to be just a preview of what is in store for the general election.
Clinton, the former secretary of state, euphorically seized the Democratic Party mantle Tuesday, seizing the nomination in dramatic fashion with primary wins in four of six states including the grand prize, California.
On perhaps the biggest night of her political career, as she declared a historic milestone for women, she assailed Trump for his divisiveness and his trademark slogan, "Make America Great Again."
"That's code for let's take America backward," she said, "back to a time when opportunity and dignity were reserved for some, not all."
"Don't let anyone tell you that great things can't happen in America," she said.
Trump laid into Clinton in his own victory speech after more primary wins, accusing her and her husband, former president Bill, of enriching themselves by "selling access, selling favours, selling government contracts."
And he signalled there would be no honeymoon, announcing a "major speech" for early next week in which he will address "all of the things that have taken place with the Clintons."
The trajectory of the race is unlikely to soar into loftier issues.
Norman Ornstein, a resident scholar at the American Enterprise Institute, fears the race will be less a battle over substance like the economy or foreign policy than a clash of two outsized personalities.
"Clinton has deep knowledge and detailed platforms, but because Trump doesn't have any, nobody focuses on the differences," Ornstein told AFP in an interview.
"And because we have two candidates who are more distrusted than trusted, more disliked than liked, this becomes a race to the bottom."
Clinton will be looking to exploit the various controversies ensnaring Trump - most recently his criticism of a Mexican-American federal judge, which sparked uproar within his own party - as a way to enhance her own resume.
"Getting down in a mud-wrestling fight with him is going to be a loser," said Tim Miller, a former communications adviser to Republican Jeb Bush, one of the many candidates defeated by Trump in the primaries.
"She has to focus on the issues that drive her base" of minorities and women and inspire young voters, Miller said.
She will appeal to moderate Republicans turned off by Trump and yet make a compelling case for supporters of her more left-leaning Democratic rival, Bernie Sanders, to embrace her campaign for victory in November.
Trump, beating Clinton to the punch, has extended an olive branch to Sanders' anti-establishment supporters, saying Tuesday: "We welcome you with open arms."
For now, Sanders has refused to capitulate, vowing to "continue the fight" to the final Democratic primary in the capital Washington next week, and then on to the Democratic convention in July.
But the Vermont senator meets on Thursday with Barack Obama - perhaps a sign that the US President will play a significant role in uniting a deeply divided Democratic party to battle the 69-year-old real estate mogul.
Obama is soon expected to offer a formal endorsement of the 68-year-old Clinton, perhaps serving to coax hardline "Bernie or bust" fans back into the party tent.
Secretary of State John Kerry, whose bid to unseat George W. Bush in 2004 ended in defeat, extended his congratulations to Clinton Wednesday, saying she "will make a terrific president" and hailing her achievement as "a truly historic moment."
Clinton won plaudits from Democrats last week in San Diego when for her blistering critique of Trump as "temperamentally unfit" to be president, a line of attack she repeated on Tuesday night.
Howard Dean, the former Vermont governor who ran for the Democratic presidential nomination against Kerry in 2004, said he was impressed with Clinton's historic achievement.
"If Hillary Clinton continues to campaign the way she did last week in San Diego, I think Trump is toast," he told AFP.