The junior U.S. senator of South Carolina, Tim Scott, is expected to announce his decision on May 22 about running for the Republican presidential nomination in 2024 as an “alternative to an alternative.”

Mr. Scott on Sunday told a crowded room of supporters at Charleston, South Carolina, “It is time to make the final step,” adding, “We will have a major announcement.”

The announcement is expected to be his official entry into the Republican primary, after forming an exploratory committee last month that allowed him to raise money for polling and other expenses related to assessing his chances.

A political scientist at John Jay College, Brian Arbour, tells the Sun that Mr. Scott is a longshot candidate at this juncture.

“Scott has a similar role to Nikki Haley, in particular, in that they’re a plausible alternative to the alternative,” Mr. Arbour said. “They’re candidates from inside the party coalition, and they’ll primarily be evaluated by party insiders.”

A recent poll from Emerson College gave Mr. Scott less than 1 percent support among Republican voters, putting him behind Governor Christie and just ahead of Governor Sununu in a hypothetical primary.

According to Mr. Arbour, however, the time to judge Mr. Scott’s presidential prospects isn’t this spring. It will be this November, when President Trump and Governor DeSantis’s campaigns have had time to play out.

Candidates like Mr. Scott are positioning themselves to be a choice for primary voters if the current frontrunners’ campaigns run aground, Mr. Arbour says.

The other reason for candidates like Mr. Scott to run, according to Mr. Arbour, is to raise their profile within the GOP. Even if Mr. Scott doesn’t win, he’ll likely be a more prominent voice after his race.

“Scott wants to be an important figure in the Republican Party and he really doesn’t want to reshape the party — he wants to take it where it wants to go,” Mr. Arbour said.

For some within the GOP, though, Mr. Scott’s entry, much like those of other long-shot candidates before him, creates a problem for those who would like to see someone beside Mr. Trump win the nomination.

The thinking goes that a larger field would give Mr. Trump an advantage because it would fracture the anti-Trump coalition in the primary election and deliver Mr. Trump the nomination.

One Republican strategist who worked on Mr. Christie’s 2016 campaign, Mike DuHaime, expressed concern over this possibility in an interview with PBS last year, when he said, “I fear it could end up the same way as 2016.”

“I think every major candidate realized that he or she would have a better shot against Trump one-on-one,” Mr. DuHaime said. “But of course each person thought he or she should be the one to get that shot and nobody got out of the way.”

Mr. Trump has proven his enduring popularity within the GOP primary electorate, bouncing back in the polls after a GOP flop in the midterms and seeing his numbers climb after being indicted on criminal charges in New York.

Mr. Arbour disagrees with what has become the conventional wisdom that a larger field benefits Mr. Trump in the primary. He suspects that Mr. Trump’s support will begin to climb as other candidates drop out.

“We see no evidence that there is a large anti-Trump coalition within the Republican primary voters,” Mr. Arbour said. “That’s over-representaed in the political conversation because anti-Trump Republicans are over-represented in the conversation.”

Mr. Arbour’s explanation for why Mr. Trump might see his support climb as candidates drop out is simple: “The average Republican voter really likes Donald Trump.

“In general the average primary voter never cares much about electability,” Mr. Arbour said. “It seems especially true with Republican primary voters in the Trump era.”