WASHINGTON — US President Joe Biden and former president Donald Trump are poised to move much closer to winning their respective parties' nominations during the biggest day of the primary campaign on Tuesday, setting up a historic rematch that many voters would rather not endure.

Super Tuesday elections are being held in 16 states and one territory — from Alaska and California to Vermont and Virginia. Hundreds of delegates are at stake, the biggest haul for either party on any single day.

In a dramatic departure from past Super Tuesdays, both the Democratic and Republican contests are effectively sealed this year.

The two men have easily repelled challengers in the opening rounds of the campaign and are in full command of their bids, despite polls making it clear that voters do 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 the majority of people in the United States do not 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.

Neither Trump nor Biden will be able to formally clinch their party's nominations on Super Tuesday. The earliest Trump could clinch the nomination is March 12; for Biden, it is March 19.

The final days before Tuesday has 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.

Favorable court ruling

After the Supreme Court ruled 9-0 on Monday to restore Trump to primary ballots following state attempts to ban him over the Capitol riot, Trump pointed to the 91 criminal counts against him to accuse Biden of weaponizing the courts.

"Fight your fight yourself," Trump said. "Don't use prosecutors and judges to go after your opponent."

The justices ruled that states cannot invoke a post-Civil War constitutional provision to keep presidential candidates from appearing on ballots. That power resides with Congress, the court wrote in an unsigned opinion.

Trump hailed the decision, declaring a "BIG WIN FOR AMERICA!!!" in a post on his Truth Social website.

The outcome ends efforts in Colorado, Illinois, Maine and elsewhere to kick Trump off the ballot because of his attempts to undo his loss in the 2020 election to Biden, culminating in the Jan 6, 2021, attack on the Capitol.

Biden is scheduled to deliver the State of the Union address on Thursday, and then campaign in the key swing states of Pennsylvania and Georgia.

The president will defend policies responsible for "record job creation, the strongest economy in the world, increased wages and household wealth, and lower prescription drug and energy costs", White House Communications Director Ben LaBolt said.

That is in contrast to Trump's "Make America Great Again" movement, LaBolt added, which consists of "rewarding billionaires and corporations with tax breaks, taking away rights and freedoms, and undermining our democracy".

Sole challenger

Trump has nonetheless already vanquished more than a dozen major Republican challengers and now has only one left: Nikki Haley, the former president's onetime United Nations ambassador who was also twice elected governor of her home state of South Carolina.

Haley has maintained strong fundraising and notched her first primary victory over the weekend in Washington, a Democrat-run city with few registered Republicans. Trump tried to turn that victory into a loss for the overall campaign, scoffing that she had been "crowned queen of the swamp".

Still, Haley winning any of Super Tuesday's contests would take an upset. And a Trump sweep would only intensify pressure on her to leave the race.

Biden has his own problems, including low approval ratings and polls suggesting that many US citizens, even a majority of Democrats, do not want to see the 81-year-old running again.

The president's easy Michigan primary win last week was spoiled slightly by an "uncommitted" campaign organized by activists who disapprove of the president's handling of the conflict in Gaza.

Ai Heping in New York contributed to this story.

Agencies via Xinhua