Disagreeing with the Truman administration's foreign policy, Bentley resigned from the diplomatic service in 1950 and returned to live in Owosso, Michigan.

[1] He was vice president of Lake Huron Broadcasting Company, Saginaw, Michigan, starting in 1952, and a director of Mitchell-Bentley Corporation.

[2][3] He was not a candidate for re-nomination in 1960,[1] instead running for a seat in the United States Senate and losing to Democratic incumbent Patrick V. McNamara in the 1960 general election.

In 1962, Bentley again ran for the U.S. House for a one-term, at-large seat created as a result of the 1960 U.S. Census, but he lost in the general election to Democrat Neil Staebler.

In 1966, while pursuing a doctoral degree, Governor George W. Romney appointed him to the board of regents of the University of Michigan.

[1] Bentley died, aged 50, while on vacation in Tucson, Arizona, of an "inflammation affecting the central nervous system".

The foundation also sponsors Operation Bentley, "a week-long intensive academic program held at Albion College for high school juniors who have been selected to participate in a rigorous and rewarding study of local, state, and national politics.

Bentley also chaired the Michigan branch of the Partners of the Alliance, an organization that had begun nationally in 1964, to act as a channel through which civic clubs, unions, business and professional groups, schools, and individuals could work directly with groups, villages, or areas in Latin America to improve the way of life in that particular area.