Ahead of the first debate between presidential candidates Kamala Harris and Donald Trump, Richard Johnson explores whether the outcome will have any real impact on voting behaviour in the US on 5 November
Conventional wisdom says that US presidential debates have little persuasive effect on voters. The vast majority of US voters already have a preferred candidate and research shows that few people change their minds after watching a debate. There are few genuine independent voters, and the US’ intensely polarised partisan environment has made the ability of one candidate to persuade supporters of the opposing candidate even more unlikely.
Given all this research, we might expect a presidential debate to have a small, marginal effect, at best, on the race. Then, the June 2024 debate between Donald Trump and Joe Biden happened. Ninety minutes ended Biden’s prospects of four more years in the White House.
In that debate, Biden defeated himself. He was rambling, incoherent, and puzzled. Biden’s physical decline from his debates against Trump in 2020 was palpable. Trump kept calm, demure, and even at points relatively dignified. It was Trump, not Biden, who called for squabbling over golf handicaps to stop and chided Biden, ‘Let’s not act like children’. Biden spat back, ‘You’re a child’.
The debate was most damaging because of what it said about Biden’s capacity to function as president. It seemed doubtful that Biden could do the job until January 2029 – the end of his second term – or even January 2025.
Negative partisanship, which refers to casting a vote to stop a party or candidate from winning, is an intense motivator in US politics
Still, even after the debate, I believed – and still believe – that Biden had a reasonable chance of winning in November. Negative partisanship, which refers to casting a vote to stop a party or candidate from winning, is an intense motivator in US politics. The polls worsened after the debate, but the position was not irrecoverable. Indeed, Biden’s energetic performances on the campaign trail after the debate were considered the starting point of a political recovery. A good convention in August and a victorious rematch against Trump in September might have been enough to erase most of the polling impact of the June debate.
Nonetheless, Biden’s exit from the race has shifted the dynamics positively for the Democrats. Trump’s modest lead has evaporated. However, the race is very close. Most national and swing state polls show the result within the margin of error. Harris is tending to be on the better side of the point estimates, giving at least an appearance of a steady lead.
Trump can win the presidency if he manages to win back just two states that he won in 2016 but lost in 2020: Pennsylvania and Georgia. Trump can afford to lose the swing states of Michigan, Wisconsin, Arizona, and Nevada. Polls have not yet shown Harris pull ahead of Trump, outside of the margin of error, in either Georgia or Pennsylvania. This means that despite the Democrats’ new enthusiasm and confidence, they are not ‘leading’ the race in a statistically meaningful way.
Despite the Democrats’ new enthusiasm and confidence, they are not ‘leading’ the race in a statistically meaningful way
It is important to note that this path to victory was not open to Trump four years ago. In 2020, if Trump had won Georgia and Pennsylvania, he still would have lost the election. Now, the same combination of states gives him the magic 270 votes. This is because states’ electoral college votes shift every ten years to reflect changes in population. The ‘red’ (reliably Republican) states have enjoyed a net gain of one electoral vote. The ‘blue’ (reliably Democrat) states have seen a net loss of one electoral vote. Among the swing states, Pennsylvania and Michigan are down an electoral vote each; North Carolina is up one. If we allocate the swing states as they voted in 2020, this means Trump is up three EVs and Harris down three EVs, simply due to population change.
Since assuming her party’s nomination, Kamala Harris has enjoyed a surge in support among Democratic voters. Harris hasn’t had a net positive approval rating since the autumn of 2021. This remains the case, but she has made considerable improvements from a year ago. In September 2023, Harris dipped below 40% positive approval, which she did not see again until August 2024. As presidential candidate, she has turned a net disapproval rating of minus seventeen to minus four.
As support for Harris has risen, so have expectations. Some judged her to be an unimpressive Vice President, attracting media attention for vacuous or incomprehensible statements. Now, many consider her an effective campaigner, attracting large crowds to her rallies and inspiring both young voters and racial minority voters who had grown increasingly disenchanted with the Democratic Party under Biden.
Harris is an effective campaigner, attracting large crowds to her rallies and inspiring both young voters and racial minority voters
Harris has so far largely avoided direct interrogation in this contest. She has only sat for one interview – pre-recorded, with her vice-presidential pick by her side, and to a friendly news channel. Consequently, her debate against Trump will be one of the first times that anyone has pressed Harris since becoming nominee about her record or policy positions.
When she ran for President in 2019, Harris had a mixed record on the debate stage. She scored some blows against Biden, notably attacking him over his record on segregation in the 1970s. She also performed well against Mike Pence in the vice-presidential debates, at one point, interjecting, ‘Mr Vice President, I’m speaking. I’m speaking’.
Harris is, it seems, much better on offence than on defence. This may reflect her background as a prosecutor. In a 2019 Democratic primary debate, Hawaii Congresswoman Tulsi Gabbard was said to have deeply irritated Harris with an attack on Harris’s record as a prosecutor in San Francisco. Gabbard is now running debate preparation with Trump, having left the Democratic Party and endorsed the man she once sought to defeat.
Debates are moments where campaigns mutually agree to set aside a degree of control in order to raise the political stakes and in the hopes of reaping a high reward. Like all gambling, skill and practice can only get you so far. Loosening control introduces greater opportunity for contingency. The US presidential race is a statistical tie and the historical pattern suggests that presidential debates tend to have a low impact on the outcome, but as the debate in June showed, history is made by contingency.
