Before the June 27 debate between Joe Biden and Donald Trump, I wrote about the history of presidential debates. I observed in that piece,

“A good performance tonight may allow Biden to close the gap below. A bad one and this gap may become permanent, creating enormous turnout problems among key elements of the Democratic base.”

A week later, the question isn’t whether Biden’s performance was a bad one—the question is whether it was fatal for his campaign. At a minimum, Biden missed an opportunity to close the enthusiasm gap that exists between Democrats and Republicans. At worst, he has ended his chances at winning, and imperiled Democrats down the ballot from U.S. Senate to state legislatures.

In some ways, the data creates a paradox. The shift from the last debate was not large in historical terms. However, the impact on the race is enormous, because the race was so close, and Biden trailed in many key states before the debate.

This update does three things:

1. It summarizes the current state of the race, and the changes since the debate.
2. It looks at those changes from an historical perspective.
3. It looks for evidence that any recent shift may unwind.

THE STATE OF THE RACE

I’ve posted a table including all of the post-debate national polling at bottom of this article. This next table summarizes that data. It is worth noting that the firms that have released new numbers since the debate were to the right of the polling average before the debate. As a result, the current post-debate margin is probably exaggerated to some degree.

A 1.9 percent change is not that big. But the implications for the electoral college are enormous.

This next table takes the post-debate polling and uses it to make projections about the state of the race in the key battleground states. The second row takes the 2020 results for each state and subtracts the change from 2020 reflected in national polling. Right now Trump leads by 3.7 percent, which is an 8.1 percent shift from 2020.

The fourth row takes the shift in margin (1.9 percent) and adjusts the current polling average in each state.

The results are dire. Using either method, Biden trails in every close battleground state, and even trails in states that were not battlegrounds in 2020. Even more ominously, U.S. Senate races are on the ballot in many of these states. Before the debate, Senate candidates were outperforming Biden by an average of nearly 7 points. But one has to wonder if even that outperformance would prevent Democrats from losing many of the contested Senate seats.

THE HISTORICAL PERSPECTIVE

My piece from last week presented the data for all of the debates. This table looks at just the first debate and adds the current polling as well as the average before the second debate.

Viewed in this context, the polling reaction from the Biden-Trump debate is quite muted. In both 2012 and 2004, Presidents Barack Obama and George W. Bush saw worse declines after their first debate. Be sure to note the irony of 2020: Biden gained a decisive advantage from his first debate against Trump.

And yet as we have seen, the fact that Biden was trailing Trump before this year’s debate makes his loss seem more dramatic. It is more dramatic in terms of its effect on who is likely to win the election.

WILL THE BOUNCE LAST?

I wrote last week:

Debate bounces often don’t last. The debates had a pretty big effect on the last two presidential races. Hillary Clinton led by 2.6 percent going into the first 2016 debate. Her lead would climb to more 8 percent after the second debate. But her pre-debate average was very close to her final popular vote margin (2.1 percent).

The same was true in 2012: Obama led by 3.8 percent going into the first debate. He even trailed after the first debate. But in the end, his final advantage in popular vote share was nearly identical to his pre-debate average.

So will this bounce unwind? And if so, when? It is impossible to know. In 2020, 2016, and 2012, the debates seemingly changed the trajectory of the race. Those bounces for the most part did not unwind until the last ten days before the election. As a result, the pre-debate averages for the last three presidential elections were actually more predictive that polling taken the week before the election.

That data suggests the change from the first debate will not be permanent, but it gives us no guidance as to when the effect will recede.

One of the largest bounces occurred in 1988 after the third debate, when then Vice President George H.W. Bush took a 17-point lead. That bounce receded by election day, but the vice president did increase his final result over the course of his debates against Michael Dukakis.

Walter Mondale picked up about 7.5 points after the first presidential debate in 1984. But in the second debate, President Ronald Reagan made a joke about his age, and in an instant turned off the issue that had cause his lead to decline. It is important to note that Mondale’s bounce was unwound by a subsequent event. The bounces in 1980 and 1976 never unwound.

In the end, every election is different. It may be that non-response bias is causing Trump’s margin to rise. It is worth remembering Trump’s unfavorable are very high, and as the debate passes from memory, the race will return to its prior state. I would actually bet on that.

But critically, Biden was trailing Trump before the debate, and he has blown one of his best chances to close that gap.

Chart containing all post-debate data available as of July 3: