How bad are Joe Biden’s post-debate poll numbers?

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Two weeks on from his calamitous debate performance, President Joe Biden is struggling to silence a chorus of senior party members and big donors urging him to end his re-election bid. Now data from polls and prediction markets can also quantify the cost of that night to his campaign.

On the day of the June 27 debate, national polling averages between Biden and Donald Trump were tied. Since then, they have sharply diverged. Trump now holds a 2.3-point lead, according to polling averages from FiveThirtyEight.

Polling in individual swing states has also tipped in Trump’s favour, with two states — Michigan and Wisconsin — flipping from a brief Biden lead back to a slight Trump advantage, according to FiveThirtyEight polling averages. Elsewhere, Trump’s advantage has widened.

In Pennsylvania, the state where Biden has spent the most on political advertisements — about $60mn for ads aired and scheduled to air since early March — the narrowing gap between the two men reversed course after June 27, with Trump on top.

Polls-based prediction models have struggled to make sense of the upended race. For example, qualitative interventions such as those from former House Speaker Nancy Pelosi and Democratic donor and actor George Clooney, who on Wednesday signalled concern about Biden remaining in the race, will not appear directly in a quantitative analysis of the race.

A model published by The Economist sees Trump as a 3-1 favourite to win November’s election, while the FiveThirtyEight model still sees the race as a coin flip. This is in part because with the election months away, polls are a noisy measure and certain “fundamentals” — Biden’s incumbency, for example — remain in his favour.

“There are many sources of uncertainty that all have to be combined properly,” FiveThirtyEight wrote on Tuesday.

Bettors and prediction markets, on the other hand, have spoken clearly about Biden’s slipping chances. His implied odds of victory, according to live trading on PredictIt, fell precipitously during the first half-hour of the debate and continued to slip as the evening wore on.

Since then, an average of a number of prediction and betting markets, published by RealClearPolitics, shows a similar downturn, and even a bouncy view on who would secure the Democratic nomination. At one point, vice-president Kamala Harris was seen as likelier than Biden.

The beneficiary of this flux: a steadily rising Trump, who these markets now see as nearly a 60 per cent favourite to win the election. Meanwhile, Biden’s chances of re-election have slipped from nearly 40 per cent before the debate to less than 20 per cent.

The biggest problem for Biden may simply be that voters think he is too old — and the older he gets the more they think so. Fifty per cent of registered voters think his age was “such a problem that he is not capable of handling the job of president”, according to a New York Times/Siena poll conducted the week after the debate; that was up from 45 per cent the week before.

As Clooney wrote of his friend Biden in The New York Times this week: “The one battle he cannot win is the fight against time.”

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