Donald Trump looked to cement his hold on the Republican presidential nomination with a sweep of Super Tuesday primaries, all but kicking off the formal campaign against President Joe Biden and an attempted shock return to the White House.
Fifteen states and one US territory were holding nomination contests, offering a huge slew of delegates. In normal election years, the day often sees one candidate emerge from a crowded field.
This time, Trump's sole remaining challenger Nikki Haley is only just hanging on, giving the scandal-plagued ex-president a chance to bury her for good.
Haley is a "lost cause," physicist Andrew Pugel told AFP at a polling station in Huntington Beach, California.
"Today's her last day," he said, though he added that it would be smart of Trump to make her his running mate and "unite the country more."
The expected Trump surge comes a day after the Supreme Court denied a bid by a handful of states to keep him off the ballot over his attack on the 2020 election, when he refused to concede defeat to Biden and sparked a mob assault on the US Capitol.
A Trump-Biden rematch in November now looks all but certain.
Biden, 81, is also on the ballot in Tuesday's Democratic primaries, but is only being challenged by little-known outsiders, making his re-nomination a formality.
On Thursday, the Democrat will address the nation in the State of the Union address to Congress, a high-profile opportunity to lay out his campaign platform and attack Trump, 77.
The states up for grabs Tuesday, which include the giant battlegrounds of California and Texas, offer 70 percent of the delegates a candidate needs to be named the presumptive nominee.
They do not officially become the nominees until they are confirmed by their party conventions later in the summer.
Trump would not be able mathematically to close out the contest Tuesday but he expects to be anointed by March 19 at the latest, according to his campaign.
Trump said over the weekend that his campaign was moving "like a rocket" towards the Republican nomination.
He made clear he is already looking past the primary, telling a rally in Richmond, Virginia: "The biggest day in the history of our country is November 5."
Trump is backed by a passionate core of supporters ready to ignore his attack on the 2020 election, judgments of liability for fraud and sexual assault, and four ongoing criminal cases.
However, Haley's campaign questioned whether middle-of-the-road Republicans will drift away from Trump by November.
"Biden's too old and Trump's a little too crazy," 70-year-old John Campbell told AFP at a polling station in Quincy, Massachusetts. But Haley, he said, "seems to be somewhat normal."
Haley, 52, lost the early nominating states to Trump, but has vowed to remain in the contest at least through Tuesday.
She also warns of the "chaos" surrounding a candidate who in just the last few months has been labeled an insurrectionist by a federal judge, and ordered to pay hundreds of millions of dollars over sexual assault and business fraud.
Trump -- who denies all wrongdoing -- also faces the threat of jail time from multiple federal and state felony charges, mostly for allegedly trying to cheat in or steal the 2020 election.
The ex-president has spent nine days in court this year alone, and complains his prosecutions are keeping him from the campaign trail -- although he has turned court appearances into part of his fundraising campaign.
Stephanie Perini-Hegarty voted for Biden in Quincy, Massachusetts.
"I think we need a leader who is not involved in any corruption, and who is going to look out for the best interests of the people. And I think that the Democrats right now are the people that do that," the 55-year-old told AFP.
