What transformed u. s. politics in the 1920s?
a. the return of the republican old guard
b. the ascent of progressive politicians
c. rising support for the democrats
d. a split in the democratic party

"A split in the Democratic Party" was one reason among the choices given in the question that transformed U.S. politics in the 1920s. The correct option among all the options that are given in the question is the fourth option or option "D". I hope that this is the answer that has come to your great help.