Swing states are states in the United States that could reasonably be won by either the Democratic or Republican candidate in a statewide election, most often referring to presidential elections. They are also known as battleground states, toss-up states, or purple states. These states are where presidential candidates focus their energy and resources throughout the campaign period. Their opposites are known as safe states, which opinion polls leading up to the election identify as being highly likely won by a particular party’s candidate.

Swing states have generally changed over time. For instance, the swing states of Ohio, Connecticut, Indiana, New Jersey, and New York were key to the outcome of the 1888 election. Likewise, Illinois and Texas were key to the outcome of the 1960 election, Florida and New Hampshire were key in deciding the 2000 election, and Ohio was important during the 2004 election. The states that voted for current Democratic President Joe Biden in 2020 and former Republican president Donald Trump in 2016 and are often highlighted as swing states include Arizona, Georgia, Michigan, Pennsylvania, and Wisconsin.

Presidential campaigns and pundits seek to keep track of the shifting electoral landscape. While swing states in past elections can be determined simply by looking at how close the vote was in each state, determining states likely to be swing states in future elections requires estimation and projection based on previous election results, opinion polling, political trends, recent developments since the previous election, and any strengths or weaknesses of the particular candidate involved.

Determining swing states is not always straightforward, and experts do not always agree on which states are swing states. The Cook Political Report sees Arizona, Florida, Michigan, Pennsylvania, and Wisconsin as toss-ups, while other experts would add New Hampshire, North Carolina, and a handful of others to the list. Political realignment from presidential election to presidential election can be one way to identify swing states. Years where a president is up for re-election tend to have fewer states that change parties, but since 1992, every presidential election has had at least a few states switch party affiliations.