Vice President Kamala Harris and former US President Donald Trump are neck and neck in polls as millions of US citizens head to voting stations on Tuesday.

Both campaigns have been laser-focused on seven key swing states that are likely to decide the eventual winner:  Arizona, Georgia, Michigan, North Carolina, Nevada, Pennsylvania and Wisconsin.

Most US states lean heavily, or at least very clearly, towards either Republicans or Democrats. Swing states – also known as battleground states – are the outliers, where support for both parties and their candidates is almost the same.

But the states that meet the bar to be categorised swing states were not always theatres that witnessed close contests.

Here is a look at how these seven states have swung in previous decades and more recent elections.

Arizona (11 Electoral College votes)

The southwestern state has long been a strong Red state. Barring Democrat Bill Clinton’s win in 1996, the state consistently voted for Republican candidates since 1952, when it backed Dwight Eisenhower.

Until 2020, when it all changed, and Biden won by 0.3 percentage points over Trump, making Arizona swing state territory.

According to poll tracking platform FiveThirtyEight, Trump is ahead in the state by 2.1 percentage points entering into Election Day. But that margin – as with all swing states this time – falls well within the margin of error for polls. The state has more Republican registered voters (34.7%) than Democrats (30.5%). Others are third-party voters.

Here’s who Arizona voted for in the past six presidential elections:

• 2000: Republican (51.0%)
• 2004: Republican (54.9%)
• 2008: Republican (53.6%)
• 2012: Republican (53.7%)
• 2016: Republican (48.7%)
• 2020: Democratic (49.4%)

Georgia (16 Electoral College votes)

This is another southern state that usually votes Republican but swung Blue in 2020. Since 1972, only two Democrats managed to win here: Jimmy Carter, who was from the state, won in 1976 and 1980, and Clinton won in his first election, in 1992.

Trump won in 2016 by five percentage points over Hillary Clinton. But Biden flipped the state, winning narrowly – by 0.2 percentage points – in 2020.

Democrats are counting on the state’s Black and immigrant population in Atlanta to help Harris clinch a win this time, while Republicans are hoping that Georgia’s majority rural and white population will pull it back to their fold. FiveThirtyEight has Trump ahead by 0.8 percentage points.

Here’s who Georgia voted for in the past six presidential elections:

• 2000: Republican (54.7%)
• 2004: Republican  (58.0%)
• 2008: Republican (52.2%)
• 2012: Republican (53.3%)
• 2016: Republican (50.8%)
• 2020: Democratic (49.3%)

North Carolina (16 Electoral College votes)

Like Arizona and Georgia, the southern state has typically voted Red.

Since Lyndon Johnson in 1964, only two Democrats have won North Carolina: Jimmy Carter in 1976 and Barack Obama in 2008.

Trump won the state in both 2016 (3.6 percent) and 2020 (1.3 percent).

He is in the lead again, although by a tiny gap – 0.9 percentage points – according to FiveThirtyEight.

One Trump campaign official, speaking to reporters last week, said it is the “one state that could bite you in the a**”, betraying the team’s nervousness over the narrow margins in the state. Trump has returned to North Carolina to campaign almost every day in the past week. A surge of early-voting Republicans gives the party some hope, analysts say.

Here’s who North Carolina voted for in the past six presidential elections:

• 2000: Republican (56.0%)
• 2004: Republican  (56.0%)
• 2008:Democrat (49.7%))
• 2012: Republican (50.4%)
• 2016: Republican (49.8%)
• 2020: Republican (49.9%)

Nevada (6 Electoral College votes)

A small state of 3 million people, Nevada enjoys a bit of a bellwether status: Barring 1976 and 2016, it has voted for the eventual winner.

Voting in recent elections has swung both ways, although since 2008, Democrats have won consistently. The state has a growing immigrant population and large numbers of third-party voters who could prove influential in shaping the outcome.

In a column this week, Jon Ralston, editor of The Nevada Independent, predicted that Harris has the edge: “There are a lot of nonpartisans who are closet Democrats.” As of Tuesday morning, Trump was ahead of Harris by just 0.3 percentage points, according to FiveThirtyEight.

Here’s who Nevada voted for in the past six presidential elections:

• 2000: Republican (49.5%)
• 2004: Republican (50.5%)
• 2008: Democrat (55.2%)
• 2012: Democrat (52.4%)
• 2016: Democrat (47.9%)
• 2020: Democrat (50.1%)

Pennsylvania (19 Electoral College votes)

It is the biggest prize among the swing states, with most Electoral College votes on offer. And many analysts believe that whoever wins Pennsylvania is likely to win the presidency – barring other surprises.

Voters in the northeast state had voted for the Democratic Party candidate consistently since Bill Clinton’s 1992 win – until Trump beat the odds, and Hillary Clinton, in the state in 2016.

The state appears deadlocked now – and both campaigns held their final pre-election rallies in Pennsylvania. According to FiveThirtyEight, Harris was 0.2 percentage points ahead, entering Election Day.

Here’s who Pennsylvania voted for in the past six presidential elections:

• 2000: Democrat (50.6%)
• 2004: Democrat (50.9%)
• 2008:Democrat (54.5%)
• 2012: Democrat (52.0%)
• 2016: Republican (48.2%)
• 2020: Democrat (50.0%)

Michigan (15 Electoral College votes)

George HW Bush was the last Republican to win the election in the midwestern state until Trump shattered predictions to win Michigan in 2016.

In 2020, Biden won the state back for Democrats, backed, among others, by the state’s large Arab American population – the largest in North America. But the community is now angry at Biden and Harris for their steadfast support for Israel’s brutal war on Gaza and Lebanon, and many have threatened to vote for Green Party candidate Jill Stein, or even for Trump.

According to FiveThirtyEight, Harris is one percentage point ahead.

Here’s who Michigan voted for in the past six presidential elections:

• 2000: Democrat (51.3%)
• 2004: Democrat (51.2%)
• 2008:Democrat (57.4%)
• 2012: Democrat(54.2%)
• 2016: Republican (47.5%)
• 2020: Democrat (50.6%)

Wisconsin (10 Electoral College votes)

Like Pennsylvania and Michigan, Wisconsin had been a reliably Democratic state for several election cycles before Trump breached that fortress to win in 2016. Before Trump, Ronald Reagan was the last Republican to win Wisconsin, in 1984.

Biden won the state back, narrowly, in 2020.

According to FiveThirtyEight, Harris is one percentage point ahead.

Here’s who Wisconsin voted for in the past six presidential elections:

• 2000: Democrat (47.8%)
• 2004: Democrat (49.7%)
• 2008:Democrat (56.2%)
• 2012: Democrat (52.8%)
• 2016: Republican (47.2%)
• 2020: Democrat (59.5%)