Dave McCormick took the oath Friday as Pennsylvania’s junior senator, bringing a new voice to Capitol Hill and giving Republicans a Senate seat in the state after two years of sole control by Democrats.

Mr. Todd, a Tennessee native and founding partner of OnMessage who coauthored “The Great Revolt: Inside the Populist Coalition Reshaping American Politics” in 2018, said it’s impossible to overstate the importance of their team not having a contested primary.

WASHINGTON, D.C. — With his hand resting on a cherished family Bible, Senator Dave McCormick was sworn into the 119th Congress on Friday in a packed chamber that blended tradition and