WASHINGTON — Sen. John Thune of South Dakota, the second-ranking Senate Republican and a potential future leader of the party, is seriously considering retiring after next year, a prospect that has set off an intensifying private campaign from other Republicans urging him to seek reelection.

Thune is only 60, but a combination of family concerns and former President Donald Trump's enduring grip on the Republican Party have prompted the senator, who is in his third term, to tell associates and reporters in his home state that 2022 could be his last year in Congress.

His departure would be a blow to South Dakota, which has enjoyed outsize influence in Washington, and could upend Senate Republicans' line of succession. Thune has been open about his ambition to lead his party's caucus after Sen. Mitch McConnell, R-Ky., makes way, and quiet but unmistakable jockeying is already underway between Thune and Sens. John Cornyn, R-Texas, and John Barrasso, R-Wyo.

"John is the logical successor should Mitch decide to not run again for leader," Sen. Susan Collins, R-Maine, said of Thune, while noting that McConnell's hold on their caucus remained "very secure."

That Thune would even entertain retirement with the chance to ascend to Senate Republican leader illustrates both the challenges of today's Congress and the shadow Trump casts over the party.

Part of Thune's hesitation owes to Trump and the potential for the former president — who lashed out at Thune early this year when the senator rejected his attempts to overturn the election — to intervene in South Dakota's Senate primary race. But the larger factor may be the longer-range prospect of taking over the Senate Republican caucus with Trump still in the wings or as the party's standard-bearer in 2024.

Thune has said he will decide his intentions over the holidays. Yet a number of his friends and colleagues have become convinced that he is serious about leaving public life.

Among those alarmed is McConnell himself, who one adviser said had "leaned in" on pushing Thune to run again.

"I certainly hope that he will run for reelection, and that's certainly what I and others have been encouraging him to do all year long," McConnell said.

He is hardly alone.

A range of Senate Republicans — from moderates and Trump targets like Collins to Trump allies like Sen. Kevin Cramer, R-N.D. — have lobbied Thune over dinner, on the Senate floor and, since lawmakers went home for Christmas recess, via text messages.

"I let him know how much I appreciate him," said Cramer, who has known Thune since they were young executive directors of their state parties. "He knows both Dakotas really need him."

Thune first angered Trump during the former president's final days in office, when Thune said any challenge to the election results "would go down like a shot dog." Trump derided the senator as "Mitch's boy" and urged Gov. Kristi Noem of South Dakota to run against him in the state's primary.

Since then, though, Trump has trained his fire on McConnell, whom he has labeled "Old Crow," and largely ignored Thune.

Two top Senate Republican allies of Trump said he would probably refrain from targeting Thune simply because the senator, who is popular at home and has a well-stocked campaign war chest, is unlikely to lose a primary in the state that first elected him to Congress in 1996.

"He likes winners, and John Thune is a winner," said Cramer, predicting that Trump would at most be "a nuisance" to Thune.

Sen. Lindsey Graham, R-S.C., was similarly blunt about why Thune need not sweat a competitive primary. "Trump worries about his win-loss record," said Graham, who is the de facto liaison between the former president and Senate Republicans.

But if Thune ascended to Republican Senate leadership, Trump could still prove a headache.

The former president does not have the influence in the Senate, where 19 Republicans defied him to support the infrastructure bill, that he does in the House. Yet Trump's regular attacks on McConnell and on anything that has the air of cooperation with President Joe Biden are not lost on Senate Republicans.

A handful of them whose seats are up in 2022, including Thune, opposed the infrastructure bill after the former president's relentless criticism of the bipartisan measure made it difficult for Senate leaders to back the legislation.

Perhaps more significant regarding Trump's future influence is the turnover in the Senate and the question of whether retiring mainstream Republicans, like Sens. Richard Shelby of Alabama, Rob Portman of Ohio and Roy Blunt of Missouri, will be replaced by Trump acolytes.

"We've just got to plow through this to the post-Donald Trump era, which I believe is coming," Collins said, lamenting that the former president's "haranguing the leader, Mitch, has gotten worse lately."

If Thune left, she said, she would "truly be beside myself."

Echoing Collins, if not as unequivocally, about why Thune should stay, Graham and Cramer both said he could eventually succeed McConnell, who will be 80 in February. Cramer said that Thune's ascension would not happen "by default" but that "it would be really good for the farm belt."

Thune has privately expressed confidence that he will have the votes to become leader whenever there is a vacancy, according to Republicans who have spoken to him.

In an interview before the recess, Thune told Punchbowl News that the possibility of becoming leader was "obviously a factor in considering whether to take another run," adding, "It's something I'm interested in."

Hoping to limit the window for any Trump interference and competition in the primary, which is scheduled for June, Thune has put off making a final decision.

Many Senate Republicans thought that was but a formality.

Thune has, however, become increasingly candid about the temptation of returning to his home in Sioux Falls, where he has young grandchildren.

In an impromptu interview this month that unnerved his supporters in South Dakota, Thune said running again would mean at least six more years of commuting to Washington — a lifestyle for which his wife, Kimberley, has little enthusiasm. "She is done with it," he told a local journalist.

If Thune retires, it would represent a striking historical symmetry in South Dakota. The state's two other best-known senators, George McGovern and Tom Daschle, both Democrats, also served three terms and left the chamber at a moment when they enjoyed enormous clout.

But both lost their reelection bids. Thune would be leaving voluntarily.

Carl Hulse contributed reporting. This article originally appeared in The New York Times.