FORT WORTH, Texas, March 5 (Reuters) - Donald Trump

aimed to deliver a Super Tuesday knockout blow to his lone

challenger for the Republican U.S. presidential nomination,

Nikki Haley, as 15 states hold Republican contests on the

biggest voting day of the primary season.

The former president, who has dominated the Republican

campaign from the start despite his litany of criminal charges,

has swept all but one of the contests so far, winnowing a

sprawling Republican field of candidates down to two.

While Trump cannot win enough delegates on Tuesday to

formally clinch the nomination, another dominant performance

would further pressure his remaining rival. Tuesday's contests

will award more than one-third of Republican delegates - and

more than 70% of the number needed to secure the nomination.

The first polls were due to close at 7 p.m. EST (0000 GMT)

in Vermont and Virginia, with voting wrapping up in Alaska at

midnight EST (0500 Wednesday GMT).

A third consecutive nomination for Trump would set up a

rematch with Democratic President Joe Biden in November's

election. Biden is expected to win Tuesday's Democratic contests

easily, though activists opposed to Biden's Israel policy are

calling on Muslim Americans and progressives to vote

"uncommitted" in Minnesota in protest.

Haley, a former U.N. ambassador under Trump, has faced

mounting questions about how long she will continue her

long-shot campaign, particularly after losing her home state of

South Carolina 10 days ago.

Her campaign did not schedule any public events on Super

Tuesday or beyond.

"As much as everybody wants to go and push me out, I'm not

ready to get out yet," she told Fox News in an interview.

Trump was leading Haley in every Super Tuesday state where

public polling data was available, according to poll tracking

website 538.

But Haley allies see a narrow window of opportunity to win

states such as Virginia, Massachusetts and Vermont, which have

more of the wealthy, college-educated voters who tend to support

her candidacy.

Trump told Fox in a separate interview that his focus was on

Biden, adding: "We're going to win every state tonight."

While Trump will stage an event on Tuesday night at his

Florida resort, Biden has no separate campaign events planned.

TAYLOR SWIFT WEIGHS IN

Pop megastar Taylor Swift encouraged her fans to vote in a

post on Instagram, though her reach may have been limited by an

extensive outage that affected that social media site and

Facebook, both of which are owned by Meta Platforms Inc ( META )

.

"I wanted to remind you guys to vote the people who most

represent YOU into power. If you haven't already, make a plan to

vote today," Swift wrote in a post that did not mention any

specific candidate by name.

Voters were also casting ballots in down-ticket races,

including two key contests in California to identify potential

successors to the late Democrat Dianne Feinstein in the Senate

and recently deposed Republican Speaker Kevin McCarthy in the

House of Representatives.

Trump's advisers have said they expect him to eliminate

Haley mathematically no later than March 19, when two-thirds of

the states will have voted. Trump is scheduled to begin his

first criminal trial six days later in New York, where he is

charged with falsifying business records to conceal hush money

payments to a porn star during his 2016 presidential run.

Haley's challenge has highlighted some of Trump's potential

vulnerabilities in a general election. She has reached 40% in

some state contests and argues that shows independents and

moderate Republicans harbor unease about a second Trump term.

"She's a solid alternative to Trump," Mac Seidel, a retired

IT worker from Southlake, Texas, said at a Haley rally on Monday

night. "She's supporting the moderates out there."

Seidel said he voted for Trump twice, but his conduct around

the Jan. 6, 2021, assault on the U.S. Capitol by his supporters

and the unprecedented 91 criminal charges facing the former

president make him an unacceptable choice now.

Trump faces both federal and state charges for election

interference, though it is unclear whether either case will

reach trial before November's election. He also faces federal

charges for retaining classified documents after leaving office,

as well as this month's hush-money trial.

Trump has pleaded not guilty in every case and claimed

without evidence that they are part of a Democratic conspiracy

to prevent him from returning to power, leveraging his legal

troubles to raise money and maintain supporters.

Katherine Meredith, a 65-year-old homemaker, voted for Trump

in California's Huntington Beach, which includes a significant

Trump base despite California being deeply Democratic.

Meredith, a two-time Trump voter, said she didn't even

consider Haley: "I don't like how she's dividing the Republican

Party. I think a lot of her issues are Democratic. I think she's

causing a big divide."