There exists a vacancy in the Eighth Congressional District of Arizona (West Valley), vice Harold Trent Franks, resigned.
The Eighth District is seen as a likely Republican hold. It re-elected Franks with 68.6% of the vote in 2016; it would flip on a 34.3% Democratic two-party swing (by this measure, the 212th seat to flip). The district gave Donald Trump a 58.1%-37.0% margin in 2016 and Mitt Romney a 61.7%-36.9% margin in 2012.
The partisan composition of the House of Representatives is now 239 Republicans and 193 Democrats, with three vacancies.