Noun
swing state (plural swing states)
(US politics) A state which may vote Democratic or Republican, in a given election or generally.
Synonyms: battleground state, purple state
New Mexico has been, in the past, a swing state. Heather Wilson
Black Fergusonians have shown that they will vote when they have something to vote for and know that their vote will count. Seventy-six percent of them turned out in November 2012, when Missouri was a key swing state for Barack Obama's reelection. Rick Perlstein