One method that made this possible was the Republican Party's imposition of the "Mountain Rule," an informal mechanism which restricted the pool of candidates.
For nearly 100 years, likely Republican candidates for office in Vermont agreed to abide by the expanded Mountain Rule in the interests of party unity.
Several factors led to the eventual weakening of the Mountain Rule, including the long political dispute between the Proctor (conservative) and Aiken–Gibson (progressive) wings of the party; primaries rather than conventions to select nominees; the direct election of U.S.
In the 1960s, the rise of the Vermont Democratic Party and the construction of Interstate 89 also contributed to the end of the Mountain Rule.
Although I-89 is a north–south route, it traverses Vermont from southeast to northwest for the majority of its length within the state and changed the way residents view how it is divided.