The Republicans are strongest in the rural Northwest, the affluent Cincinnati and Columbus suburbs, and have made gains in Appalachian Southeast Ohio and the industrial, working-class Northeast in the 21st century.
The Democrats rely on the state's major cities, and have made gains in educated suburban areas in recent years.
Since 1896, however, Ohio has voted for the winning candidate, except for Franklin D Roosevelt in 1944, John F Kennedy in 1960, and Joe Biden in 2020.
Due to a close split in party registration, it has been key battleground state.
The state was closely contested in 2008 and 2012, with Barack Obama winning narrowly on both occasions.