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The bounce presidential nominees ride out of conventions has been shrinking for decades. Today, Donald Trump can consider even a 1-point bump a victory emerging from the Republican National Convention in Cleveland. His predecessor, Mitt Romney, saw a one-percent dip in his polling leaving his convention in 2012 in Tampa, Fla.
There are two main ways to evaluate these post-convention bumps. First, it's a question of how big of a bump a candidate gets, and the one of how durable that bump is. Some pundits look at the size of the bump and whether or not it exceeds the “par” of about 5 to 6 points. Still others look at how long into the late summer or early fall the bump lasts.
In the past, conventions have produced, on average, around a 5 to 6-point bump, based on where the candidates were polling before the convention to where they were after the event. Going back to 1964, only three conventions (Democrats in 1972 and 2004, and Republicans in 2012) have had a net negative or flat bounce for their nominees.
In general, there’s no right or wrong way to look at the numbers, but regardless of whether you’re looking at the size of the bump, or the longevity, keep in mind that every year is different. Comparing one election to another is not exactly an apples-to-apples comparison.
There’ll also be a lag in the measurement, so while we’re waiting for polling results to come back from Cleveland keep an eye on social media and the news coverage. Since most Americans won’t be watching the conventions on television, the narrative in the media around the events in Cleveland and subsequently Philadelphia is where many voters will frame their opinions. That’ll ultimately lead to a bump, or drop in the polls.
Also complicating the numbers this year, is the situation where the conventions are back-to-back. Before 2004, the conventions were typically separated by a few weeks. Often times one party would hold their convention before the Olympics and the other after.
This allowed a much cleaner read on the data and allowed us to see the exact movement in the polls, which was attributable to the convention itself. This year pollsters will start their post-GOP polling on Saturday and typically have results Tuesday or Wednesday morning. That means at least one if not two nights of calling will be done during the start of the Democratic convention, which may or may not have an effect on the numbers. But it will be incredibly difficult to tell either way.
Whatever criteria you use to measure the bump, there’s no doubt that this election cycle’s conventions are extremely important to both party’s candidates. Trump, however, has perhaps the most to gain and the most lose.
Each presidential cycle, the goals of the conventions are to present a unified party, set the tone for the rest of the campaign, control your own narrative, and present your vision of America directly to voters. That’s not exactly a description of what happened in Cleveland, which could spell trouble because Trump had a hill to climb going into the confab.
According to a NBC/WSJ poll taken right before the Republican convention, 85 percent of Americans say the Republican Party is not unified, and Lincoln Park Strategies’ recent national poll showed that just 69 percent of registered Republicans say they’re currently supporting Trump. Ted Cruz’s speech likely didn’t help move those numbers.
This was Trump’s biggest and best shot at bringing these disaffected Republican’s back into the fold. But if his Thursday night speech fails to consolidate these base Republican voters, expect a smaller-than-average bump that will linger over his polling numbers through the campaign season.
Meanwhile, it could be argued that Hillary Clinton only has one main challenge — showing that the Democratic Party is unified behind her.
Our national survey of registered voters in late June showed Clinton winning 79 percent of Democrats. With Bernie Sanders having already endorsed Clinton since then, and with his primetime convention speaking slot already set, Democrats are well on the way to bringing the party together behind the party’s nominee.
Given Clinton’s relatively low bar and the fact that the Democratic convention is going second, we would expect to see a small uptick in her polling in the week after Philadelphia. What will happen with Trump’s numbers is incredibly hard to predict so we’ll have to wait on the numbers.
All this being said, we’ve not seen any major movement in the polls since 1992 when the country was being introduced to Bill Clinton for the first time. In the days of the 24-hour news cycle, and the prevalence of social media, most voters have made up their minds.
Regardless of how well a convention goes or doesn’t, it’s hard to swing the numbers in a meaningful fashion in a short period of time.
Stefan Hankin is founder and president of Lincoln Park Strategies, a Washington D.C.-based public opinion firm. Follow him on Twitter at @LPStrategies.