2017 Montana's at-large congressional district special election
In Montana, an at-large congressional district special election was held on May 25, 2017, to determine the member of the United States House of Representatives for Montana's at-large congressional district. The election was necessitated by incumbent Republican Representative Ryan Zinke's appointment as United States Secretary of the Interior.
Source: Wikipedia — 2017 Montana's at-large congressional district special election (CC BY-SA 4.0)