Biden, Trump dominate Super Tuesday, cruise toward nomination and rematch

US President Joe Biden and his predecessor Donald Trump have swept the coast-to-coast contests on Super Tuesday, all but cementing a November rematch and increasing pressure on the former president's last major rival, Nikki Haley, to leave the Republican race.

Biden and Trump each won Texas, Alabama, Colorado, Maine, Oklahoma, Virginia, North Carolina, Tennessee, Arkansas, Minnesota and Massachusetts. Biden also won the Democratic primaries in Utah, Vermont and Iowa.

In Minnesota's Democratic primary, "uncommitted" votes surged close to 20 percent, surprising many with less than a week of organising. Previously seen as negligible outside Michigan, the impact of "uncommitted" votes is likely to be significant for Biden.

For the Republicans, Haley's strongest performance was in Vermont, where she scored a surprise victory, upsetting Donald Trump. That victory will do little to dent Trump's primary dominance, however.

The former president won 11 other states on Super Tuesday. Trump carried other states that might have been favourable to Haley such as Virginia and Maine, which have large swaths of moderate voters like those who have backed her in previous primaries.

Trump described the results as "an amazing night" as he closed in on becoming the party's nominee.

"They call it 'Super Tuesday' for a reason," Trump told the crowd gathered at his Florida estate. "This is a big one. They tell me, the pundits and otherwise, that there has never been one like this, never been anything so conclusive."

Super Tuesday elections were held in 16 US states — from Alaska and California to Vermont and Virginia. With hundreds of delegates at stake, this was the biggest haul for either party on any single day.

"If we lose this election, you're going to be back with Donald Trump," Biden told DeDe McGuire, a radio host, earlier in the day.

Later Biden warned that Trump was "determined to destroy" US democracy.

Trump "is determined to destroy our democracy, rip away fundamental freedoms like the ability for women to make their own health care decisions, and pass another round of billions of dollars in tax cuts for the wealthy — and he'll do or say anything to put himself in power," Biden said in a statement released by his campaign.

Mental acuity for the top job

Despite Biden's and Trump's domination of their parties, polls make it clear that the broader electorate does not want this year’s general election to be identical to the 2020 race.

A new AP-NORC Center for Public Affairs Research poll finds a majority of Americans don't think either Biden or Trump has the necessary mental acuity for the job.

"Both of them failed, in my opinion, to unify this country," said Brian Hadley, 66, of Raleigh, North Carolina.

The final days before Tuesday demonstrated the unique nature of this year’s campaign. Rather than barnstorming the states holding primaries, Biden and Trump held rival events last week along the US-Mexico border, each seeking to gain an advantage in the increasingly fraught immigration debate.

Trump recently told a gala for Black conservatives that he believed African Americans empathised with his four criminal indictments.

That drew another rebuke from Democrats around the country for comparing personal legal struggles to the historical injustices Black people have faced in the US.

The former president has nonetheless already vanquished more than a dozen major Republican challengers and now has only Haley left.

She has maintained strong fundraising and notched her first primary victory over the weekend in Washington, DC, a Democrat-run city with few registered Republicans. Trump scoffed that Haley had been "crowned queen of the swamp."

"We can do better than two 80-year-old candidates for president," Haley said at a rally Monday in the Houston suburbs.

Vulnerabilities with influential voter blocs

Trump's victories, however dominating, have shown vulnerabilities with influential voter blocs, especially in college towns like Hanover, New Hampshire, home to Dartmouth College, or Ann Arbor, where the University of Michigan is located, as well as areas with high concentrations of independents.

That includes Minnesota, a state Trump did not carry in his otherwise overwhelming Super Tuesday performance in 2016.

Biden has his own problems, including low approval ratings and polls suggesting that many Americans, even a majority of Democrats, don’t want to see the 81-year-old running again. The president’s easy Michigan primary win last week was spoiled by an “uncommitted” campaign that disapproved of the president’s handling of Israel’s war in Gaza.

Allies of the "uncommitted" vote are pushing similar protest votes elsewhere, including Minnesota. The state has a significant population of Muslims, including in its Somali American community.

In Massachusetts, 29-year-old Aliza Hoover explained her "no preference" vote as a principled opposition to Biden's approach to Israel but said it does not necessarily reflect how she will vote in November.

"I think a vote of no preference right now is a statement to make yourself a single-issue voter, and at the moment the fact that my tax dollars are funding a genocide does make me a single-issue voter," Hoover said.

"I would love to see the next generation move up and take leadership roles,” said Democrat Susan Steele, 71, who voted Tuesday for Biden in Portland, Maine.