WASHINGTON—Republican senators’ secret ballot vote Wednesday for a new leader will test how much lawmakers want to shake things up as they enter an era defined by the populist energy that propelled President-elect Donald Trump back to the White House.

Senate Minority Whip John Thune will be the new Republican Senate leader and the majority leader of the upper chamber in the new Congress. In January, he will succeed Senate Minority Leader Mitch McConnell,

Senate Republicans will elect a new leader to replace Kentucky Sen. Mitch McConnell, stepping aside after 17 years at the top of the Senate GOP. Three candidates are vying to replace McConnell: South Dakota Sen.