What Are Swing States and Why Are They Critical in US Elections?

Swing states, also known as battleground states or purple states, are highly competitive states that have historically swung between voting for different parties in presidential elections. While most states consistently vote along party lines—from 2000 to 2016, 38 states voted for the same political party—the few who don’t receive an outsized amount of attention from candidates and pollsters. Here’s the history of swing states and the powerful influence they’ve had on elections in America.

The Founding Fathers were divided on how to pick a president. Some wanted Congress to select the nation’s leader, while others wanted to citizens to vote directly. The Electoral College was created as a compromise. The Constitution grants each state a number of electors based on the combined total of the state’s delegates in the Senate and House of Representatives. There are 538 electoral college votes total, and presidential candidates need 270 electoral votes to win the White House. Forty-eight out of 50 states have a “winner take all” system, meaning that whoever gains the popular vote wins all of that state’s electoral college votes. Two states—Maine and Nebraska—use the congressional district method, meaning they allocate two electoral votes to the popular vote winner in the state and one electoral vote to the popular vote winner in each Congressional district.

Presidents can win the popular vote and lose the electoral college vote. It’s happened five times, most recently in the 2016 election, when Hillary Rodham Clinton received 2.8 million popular votes than Electoral College winner Donald Trump, the largest disparity in history.

Because 38 out of the 50 states have voted for the same party since the 2000 presidential election, it’s relatively easy to predict which states will vote for a Democratic candidate and which will vote for a Republican. It is the states that do not consistently vote along party lines that determine whether a candidate will win or lose: Swing states.

There is a reason why swing states exist in the United States—the U.S. voting system is structured around states. As John Hudak, a senior fellow at the Brookings Institution explains, “Our presidential election system is designed to make states the important jurisdictional unit in voting."

Hudak credits the highly competitive 1800 presidential election between Aaron Burr and Thomas Jefferson as heightening political interest in winning over specific states.

“After 1800, states began to take a firm approach to making sure that their numbers were both collected and reported. As time went on, politicians got to know what state constituencies looked like, and that competitiveness grew as well,” says Hudak.

David Schultz, editor of Presidential Swing States: Why Only Ten Matter with Stacey Hunter Hecht, says swing states began to really emerge in the wake of the Civil War. “In 1860 it’s the slavery issue that creates swing states like Ohio,” says Schulz. He explains that the Republican Party had been founded only a few years earlier in Wisconsin, and it was taking off in the Midwest. The party became known for supporting abolition and keeping the Union together.

"Northern states vote for Lincoln. Southern states vote for the democratic candidate. It’s states like Ohio that tipped the balance,” he says. “No Republican has won the presidency unless they’ve won Ohio,” says Schultz.

While the concept is nearly as old as the Electoral College, the term “swing state” is a relatively modern creation, first used by the New York Times in 1936 while Franklin D. Roosevelt was campaigning in the West. It didn’t pick up steam until the hotly contested 2000 election, when journalists covered battleground states like Florida with increasing fervor.

The claim that “every vote counts” is especially true in swing states. Close presidential elections throughout American history have borne this out: Harry S. Truman defeated Thomas Dewey in 1948 by winning by less than one percent of the popular vote in then-swing states like Ohio, California, Indiana, Illinois and New York—a race so close that newspaper headlines mistakenly proclaimed Dewey the winner.

In the 1960 presidential election between Richard M. Nixon and John F. Kennedy, 10 states were won by less than two percent of the vote. And in 2000, the results of the election came down to who won Florida, which George W. Bush claimed by a margin of just 537 votes.

The high-stakes game of winning over swing states means candidates spend 75 percent or more of their campaign budget on courting them. Candidates almost exclusively visit swing states on the campaign trail, often skipping other states entirely unless they’re fundraising. “Swing states are the presidential campaign,” says Hudak.

There are three main factors that can create swing states, and they often overlap and are all at play.

1. Population Changes. Urban areas tend to vote Democratic and rural areas tend to lean Republican. When citizens leave liberal-leaning coasts or major cities to settle in smaller cities or more rural areas, they can alter the balance between parties.

2. Ideological Polarization: The Pew Research Center has found that the ideological divide between parties began to widen in the 2000s. “Before the 1990s, there was a good number of liberal Republicans in the North and conservative Democrats in the South," says Hudak. "As parties divide, they can change whether a state is a swing state or not."

3. Moderate Politics: In a state with more moderate voters, the divide between Republicans and Democrats narrows, making it more difficult to determine political outcomes. Hudak says that states including Maine and New Hampshire "have a lot of moderate, independent-minded voters...who drive that two-party competitiveness."

Hudak adds that as the country has evolved, the number and identity of swing states has evolved as well. “The Voting Rights Act has had a huge impact on enfranchising African Americans who couldn’t vote 50 years ago in places like Texas, North Carolina, and Georgia,” says Schultz.