The affable traditional conservative from South Dakota is the first new chief of the Senate G.O.P. in nearly two decades. He will confront a challenge managing President-elect Donald J. Trump’s expectations.

New Senate Majority Leader John Thune is kicking off the new session with a promise to preserve the filibuster, saying in his first floor speech as leader that his priority will be to “ensure the Senate stays the Senate.

Sen. John Thune (R-SD) will promise to maintain the filibuster on Friday afternoon in his first speech as Senate majority leader. “One of my priorities as leader will be to ensure that the Senate stays the Senate,