A few days after losing the Senate primary, Rankin was appointed to fill a vacancy as an associate justice of the Montana Supreme Court, a position he held until the end of 1925.

He resigned that post to accept an appointment from President Calvin Coolidge as U.S. Attorney for the District of Montana (i.e. the entire state).

Rankin was the unsuccessful Republican nominee for governor in 1928, but continued as U.S. Attorney; he was re-appointed to that post by President Herbert Hoover in 1930 and served until 1934.

[4] He returned to practicing law until 1942, when he ran for the U.S. Senate against liberal incumbent Democrat James Edward Murray.

Her vote against the United States entering World War II was highly unpopular, and resulted in her retirement.