Haley's campaign said on Wednesday it was rolling out digital ads and mailers that would raise doubts about both Trump and Biden's mental acuity, criticize them for not campaigning more vigorously and cast them as profligate spenders.

Haley, who is 52 and a former ambassador to the United Nations, has made age and mental fitness for the presidency an issue in the race like few politicians in the modern era. Saying it is time for a new generation of leadership in Washington, she has called for competency tests for politicians older than 75 and is an advocate for term limits for lawmakers.

Her argument may carry some resonance in an election where the president is 81 and his likely challenger, Trump, is 77, and where many Americans say they are frustrated by their lack of options.

The title of Haley's new attack campaign is modeled after the 1993 hit comedy starring Jack Lemmon and Walter Matthau as cantankerous seniors. Upcoming episodes include titles such as "Stumbling Seniors" and "Debate Dodgers," her campaign said.

"Sadly, this version of Grumpy Old Men offers no comic relief -- just chaos, confusion and a bad sense of deja vu for the American people," said Haley spokesperson Olivia Perez-Cubas.

Campaign spokespeople for Trump and Biden, who have also at times questioned the other's competence, did not respond to a request for comment on the new Haley effort.

A Reuters/Ipsos poll released last week showed widespread apathy among the electorate about a 2024 rematch between the president and former president, along with deep concern about both men's fitness for the job.

According to the poll, 67% of respondents said they were "tired of seeing the same candidates in presidential elections and want someone new." And 75% of poll respondents agreed with a statement that Biden was too old to work in government, while half said the same about Trump.

On the campaign trail, Haley has long mocked Biden's mental fitness. In New Hampshire earlier this month, she began lumping Trump and Biden together.

Haley suggested Trump was suffering from cognitive decline after he apparently confused her with former House of Representatives Speaker Nancy Pelosi in remarks during a rally.

"Do we really want to go into an election with two fellas that are going to be president in their eighties?" Haley told a crowd in Keene, New Hampshire.

That strategy was not enough for her to avoid an 11-percentage-point loss to Trump in the state's Jan. 23 primary.

Exit polls in New Hampshire showed that Haley didn't do particularly well with younger voters. Both she and Trump appealed almost equally across age groups, with Trump winning nearly every single category by similar margins.

Trump at a campaign event in Nevada on Sunday addressed Haley's criticisms, saying he felt "sharper now than I did 20 years ago."

Trump has also taken to mocking Biden's age on the campaign trail, sometimes doing a pantomime on stage where he walks around with a dazed look on his face. His rallies routinely show video images of Biden stumbling.

Biden has gone after Trump as well, saying at an event in South Carolina on Saturday that Trump is "growing a little confused these days."

Haley, the only remaining Republican in the race with Trump, will send mailers from her new series to voters in South Carolina, where the next major Republican primary takes place on Feb. 24.

While Trump remains favored, Haley is hoping to pull of a surprise in a state where she served six years as governor.

Rob Godfrey, a former Haley aide in South Carolina who has remained neutral in the primary, said Haley's approach could benefit her with voters bothered by the lack of choice, even in states with a significant number of older voters.

"Nikki Haley has made a generation change argument one of the signature parts of her campaign," Godfrey said. "As she sharpens contrasts with her opponents, I expect her to keep this one up."

(Reporting by James Oliphant; Editing by Colleen Jenkins and Alistair Bell)

By James Oliphant