The second-ranking Senate Republican will endorse fellow Sen. Tim Scott (R-SC) later Monday at his 2024 presidential campaign launch in South Carolina, according to a source familiar with the matter.

John Thune (R-SD) is expected to attend and deliver remarks at Scott’s campaign kickoff event in North Charleston, three days after the 57-year-old filed paperwork to run for the White House.

Thune, 62, will join fellow South Dakota GOP Sen. Mike Rounds, who endorsed Scott last week.

Scott, the only black Republican in the Senate, will enter the race with $22 million in cash on hand — the most of any presidential hopeful in history, according to the Federal Election Commission.

Florida Gov. Ron DeSantis is also preparing to jump into the race this week after groups supporting him received around $110 million in donations.

Both Scott and the 44-year-old DeSantis have visited Iowa and New Hampshire in recent weeks to gauge Republican support in the two early-voting states. Scott is also set to roll out a $5.5 million ad buy in both states timed to his campaign announcement.

The South Carolina Republican will face off against the former governor of his home state, Nikki Haley, as well as former President Donald Trump, who currently leads in the polls.

Longshot candidates such as entrepreneur Vivek Ramaswamy, former Arkansas Gov. Asa Hutchinson, conservative radio host Larry Elder and businessmen Perry Johnson and Ryan Binkley have also entered the race.

Former Vice President Mike Pence, who broke with Trump following the Jan. 6, 2021 Capitol riot, has yet to announce his widely anticipated presidential run.

Thune is on record reproaching the 76-year-old ex-president for his attempts to overturn the 2020 election, saying in December of that year that any challenge of results in the upper chamber would “go down like a shot dog.”

As was the case with several other Republicans who refused to back Trump’s unsubstantiated claims of a stolen election, Thune drew the ire of the former president, who then threatened that the senator’s political career would be over. 

However, Thune easily won re-election last year.

After outlasting Trump’s failed attempt to oust him from Congress, Thune has said it is time for the GOP to move beyond the former president’s obsession with the 2020 election, saying in November that “it’s clear that running on relitigating the 2020 election is not a winning strategy.”

The following month, Thune expressed approval of a potential Scott presidential run.

“He’s obviously helped a lot of people around the country in the last year, raised a lot of money and built a lot of relationships that can be very useful if he does [run],” he told Politico at the time.

“Our nation needs and deserves a leader who can unite our country. I’m confident that Senator Tim Scott is that leader,” Rounds told The Post in a statement, favorably comparing the senator to former President Ronald Reagan. “The last several years have clearly demonstrated that we need competent, conservative leadership in the White House.”