Historically, presidential candidates as unpopular as Donald Trump faced decimation in the electoral college. But thanks to the increasing polarization of both parties and voters, that has become a thing of the past

The map of competitive states is expanding this year as Donald Trump’s poll numbers dipped to surprising lows in historically red states such as Georgia and Arizona. The last time either state voted Democratic was two decades ago.

But even as the small club of battleground states grows this year, fewer than 10 states will likely determine the outcome of this year’s race.

Relying on the same handful of states to decide the outcome of presidential elections is a fairly recent phenomenon. Just three decades ago, when politics weren’t yet so polarized, all 50 states were up for grabs, swinging between parties from one election to the next.

Looking somber and drained near midnight on 6 November 1984, Democrat Walter Mondale conceded victory to Ronald Reagan in the presidential election after Reagan won 49 of 50 states. Mondale won only his home state of Minnesota.



Such blowout elections may seem incredible today, but Reagan’s win was less exceptional at the time. Just 12 years earlier, in 1972, Richard Nixon also swept 49 out of 50 states against George McGovern to become president. And in 1964, Lyndon B Johnson won 44 states to Barry Goldwater’s six.



That’s in stark contrast to today’s political landscape.



Despite campaign troubles and low favorability ratings, Trump will almost certainly win at least 20 states, if not 25 – half the US – on election night. In a different decade, a candidate plagued by controversial statements, with a historically underfunded campaign, and who many party elites have publicly denounced might have been tanking in more states.

The term “swing states” is well known today, but the same few states determining several consecutive presidential elections is a recent occurrence.

The phrase “swing state” wasn’t mentioned in books until the 1950s, according to Google Ngram Viewer, a service that shows how often phrases have been used in texts over time. But between 2000 and 2008, usage of the term more than tripled. During that period, Ohio, Florida, Virginia and a handful of others coalesced into the group we now think of as swing states.



Since 2000, 40 states have voted for the same party’s candidate in all four presidential elections. By contrast, in the four elections between 1984 and 1996, states “swung” more often: only 17 states voted for the same party’s candidate in the four consecutive elections during that period.



Increasing political polarization is a big factor in the swing state phenomenon. The roots of current polarization stretch back to about the 1970s; since then, the parties have become not only more ideologically sorted but also more ideologically divergent, and their members more hostile toward the opposing party.

Liberal Republicans and conservative Democrats used to make up a much larger share of both the US Congress and the broader population. Even a decade ago, conservative Democratic representatives in Congress voted alongside Republicans almost as often as they voted alongside Democrats. Now, conservative Democrats in the House and Senate have been unseated by Republicans, and liberal Republicans have lost their seats to Democrats.



It’s also increasingly rare for members of either party to break party lines when voting, both for ideological reasons and as strategic moves in an increasingly intense competition for party control.

Voters’ ideas are also becoming more homogenous and more in sync with their chosen party’s platform. In 1994, Pew Research Center found that only about one in 10 Americans expressed views across a range of issues that were either consistently conservative or consistently liberal. Today that number is one in five. Both parties’ median ideologies have also drifted apart between 1994 and 2016, which means there is less common ground between the parties.

In addition to increasing ideological differences and greater ideological sorting, Republicans and Democrats have much more animosity toward one another today compared to 20 years ago.

In another 1994 Pew survey, about one in five Americans on either side of the political aisle reported having a “very unfavorable” view of the opposing political party. Today that number has increased to three in five. When just “unfavorable” views are added in, around 90% of Americans report having unfavorable or very unfavorable views of their political opponents.

Americans’ strong distaste for the opposing party and growing ideological gap mean that today’s voters aren’t likely to switch between parties frequently, if at all.

But the way a state votes is not immune to long-term change. Demographic shifts – including growing urbanization, migration and an ageing population – mean that the swing states of the future may be different than the swing states of today. But unless politics become vastly less polarized, swing states are here to stay.