Senator John Thune of South Dakota emerged victorious over a right-wing, MAGA-backed challenge from Senator Rick Scott of Florida.

© Tom Brenner for The New York Times

The president-elect is to visit Capitol Hill on Wednesday as Republican senators elect a majority leader. His staffing decisions are already depleting the narrow majority the G.O.P. expects in the House.

© Scott McIntyre for The New York Times

Advisers to the president-elect, who already has a strong hold on congressional Republicans, want him to tighten his grip by torpedoing the bid of the establishment front-runner for the post.

© Kenny Holston/The New York Times

Senators Rick Scott, John Thune and John Cornyn quickly responded to President-elect Donald J. Trump’s demand on social media, the latest example of his influence over Republican lawmakers.

© Kenny Holston/The New York Times