Will the Debate Knock Trump Off the Comeback Track?

Will the Debate Knock Trump Off the Comeback Track?
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Is Donald Trump on track to win the presidency? Or can Hillary Clinton simply hold onto her lead in the polls and run out the clock?

A month ago (when Clinton was ahead by about five points in the two-way RealClearPolitics average), I asked similar questions and used past presidential election polling to create benchmarks for a potential Trump comeback. The idea was to develop some simple, data-driven rules of thumb indicating how plausible a Trump comeback or win might be given his standing in the polls on a given date.

The guidelines were fairly simple -- Clinton's lead in August was not too big to overcome before Election Day; he would want to be within a few points by late September; and there isn't much time to move polls significantly in October. September is now nearly over, so it’s worth revisiting that data to assess how plausible a Trump comeback is given the current polling.

That data indicates Trump had been hitting or exceeding his benchmarks for nearly a month, but Clinton’s strong debate performance  puts him at risk of barely making or even missing those to come.

The data behind the benchmarks is summarized here:

This graphic shows how much an average of polls on a given date differed from the final polling average heading into Election Day. The black line shows the trend -- essentially, that’s how much polls typically can move in a given interval before Election Day. More details on the data, how I accounted for conventions and how the trend line was calculated can be found here.

For most of September, Trump has been exceeding his benchmarks. Clinton led him in the RCP averages for all of this month, but historical data suggested that her lead was small enough that the GOP nominee could still overtake her before Election Day. Heading into the debate, Clinton led by about two percentage points (the exact number changes if third parties are/aren’t included), which meant that Trump could realistically still catch up.

But post-debate polling suggests the Democratic nominee may have improved her standing. Rasmussen Reports released a poll Thursday that showed Clinton ahead of Trump by one point. This is a significant improvement from Rasmussen’s poll last week, which had Trump leading by five. Public Policy Polling (a Democratic firm) also released a post-debate survey that put Clinton ahead of Trump by four points. PPP’s last survey showed her ahead by five, but it was conducted in late August. At that time, Clinton was leading Trump by about four points in the RCP poll averages rather than one or two. Additionally, many polls have shown that voters believe Clinton won the debate by a large margin, and debate wins do sometimes lead to bounces in the polls.

If polling data continues to show such a bounce, it will likely keep Trump from exceeding his benchmarks and may even put him behind on them. If the debate ends up improving Clinton’s standing by about two points, then Trump will be at a four-point deficit. He would then just barely hit his late September/early October benchmark. If Clinton’s bounce is larger than two points, Trump will miss his benchmarks by a significant amount. He could still win despite missing the benchmarks, but he would have to make up ground more quickly than most of his predecessors have been able to do.

A few caveats: Most of the major pollsters still haven’t released post-debate polls. Although early evidence suggests a bounce for Clinton, upcoming polls might reveal that it was a mirage. If that ends up being the case, she will likely hold a small lead but that lead will not be safe. It’s also important to note that this a volatile contest. Seemingly random events (e.g. Trump’s controversial statements and Clinton’s ongoing email and ethical issues) have moved public opinion, and a large number of voters are undecided or choosing third party candidates. That means the polls could move more quickly in this race than in recent races. Note that this volatility cuts both ways -- it gives Trump a greater opportunity to catch up to Clinton, but it also gives Clinton the chance to turn a small or decent lead into a solid win or even a landslide.

Finally, it’s important to note one other feature of the historical data:  Both candidates’ ability to move the polls diminishes as October wears on. If Clinton gets and keeps a decent post-debate bounce, that’s bad news for Trump. In that case, Clinton might be able to simply run out the clock. But if her bounce fades, if Trump regains ground in upcoming debates or if more damaging information about Clinton’s emails come to light, she may be stuck in a close race or at a deficit with little opportunity to improve her standing.

David Byler is an elections analyst for RealClearPolitics. He can be reached at dbyler@realclearpolitics.com. Follow him on Twitter @davidbylerRCP.

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