Career
He was a Democrat. In 1936 he decided not to run for reelection and instead challenged Democratic incumbent United States senator James East. Murray in the Democratic primary. Murray soundly defeated Monaghan and Republican T.O. Larsen. Murray received 55% of the vote, Larsen 27% of the vote and Monaghan 18%.
At the age of 30, Monaghan"s political career came to an education
He returned to his law practice, and returned to politics only briefly in 1964 when he ran for the Democratic nomination unsuccessfully for the United States Senate in Montana, against Senate Majority leader Mike Mansfield.