Two curmudgeonly old rivals, reclusive spendthrifts, are marching toward a showdown that a lot of people really wish wasn’t happening. If that is the plot of a slapstick comedy, it’s also the latest knock from Nikki Haley on former President Donald J. Trump and President Biden as she fights for oxygen ahead of the Republican primary in South Carolina on Feb. 24.

In a new series titled “Grumpy Old Men,” the Haley campaign on Wednesday plans to start unveiling online videos, digital ads and voter emails that will underscore the ways in which Ms. Haley has argued that the two party front-runners are alike. The episodes, with titles like “Stumbling Seniors,” “Basement Buddies” and “Profligate Pols,” take shots at, among other things, her rivals’ signs of mental confusion, their light presence on the campaign trail and their economic policies leading to high inflation.

The push is part of a shift in strategy that Ms. Haley began after the Iowa caucuses, casting Mr. Trump, 77, and Mr. Biden, 81, as belonging to the same bygone era of politician, one she says is deeply at odds with the country’s needs. It also follows her more aggressive posturing toward Mr. Trump as the two head into a heated face-off in South Carolina, the state where she was born and raised, and which she led as governor.

But the series, with its reference to a movie from 1993, could prove a risky bet as she looks to court a Republican base that is largely graying, white and Christian. Polls show her trailing the former president by double digits in her home state. Attacks on Mr. Biden’s age did not play well during the 2020 Democratic presidential primary.

Ms. Haley, 52, who served as a United Nations ambassador under Mr. Trump, has consistently pitched herself as a “new generational leader” for her party and called for mental competency tests for candidates who are 75 or older. Yet, until recently, she has taken a careful approach toward both men and their age.