WASHINGTON—Republican senators chose John Thune of South Dakota as their first new leader in nearly two decades, opting for continuity over calls for radical change heading into populist President-elect Donald Trump’s second term in the White House.

The election of Republican John Thune of South Dakota as Senate majority leader tasks a key ally of Mitch McConnell with shepherding the agenda of President-elect Donald Trump through Congress.

John Thune, John Cornyn and Rick Scott are vying to succeed Mitch McConnell as the Republicans leader in the U.S. Senate.