Michael Crapo launched his political career in 1984, winning a seat in the state Senate that had been expanded from 35 to 42 members through reapportionment.
He was re-elected in 1986 and served as Republican floor leader before being elected president pro temp in 1988 and again in 1990. He was elected to the U.S. House in 1992 with 63 percent of the vote, defeating Democrat J.D. Williams and two other candidates.
He was re-elected in 1994 with 75 percent of the vote, defeating Democrat Penny Fletcher. In 1996, Crapo was re-elected with 69 percent of the vote against Democrat John Seidl. Crapo was elected to the U.S. Senate in 1998, defeating Democrat Bill Mauk with nearly 70 percent of the vote. The seat opened up when incumbent Dirk Kempthorne ran successfully for governor.
Democrats failed to put up a challenger against Crapo in the 2004 Senate race, effectively conceding the race.