Democratic presidential candidate Hillary Clinton and US vice president nominee Tim Kaine stand with their families at the end of the fourth day of the Democratic National Convention at the Wells Fargo Center, July 28, 2016, in Philadelphia.
CNN  — 

The major party political conventions have historically been the turning point in many campaigns. In 1988, Democrat Michael Dukakis entered the conventions as the frontrunner, only to leave trailing Republican George H.W. Bush. Four years later, Bush was barely ahead of Democrat Bill Clinton, but Clinton left the conventions with an advantage he never gave up.

This year, I’d be betting on something different to happen. While it’s conceivable the conventions could produce a game changing moment, there are three reasons why I’m skeptical they will.

First, convention bounces have been getting smaller over the last few decades. Since 2004, the average convention bounce has been just 2 points. Some years, it’s been even less. Compare that to the 1968 to 2000 period. According to Geoffrey Skelley at FiveThirtyEight, the average bounce during that 32-year period was a little less than 7 points.

Right now, former Vice President Joe Biden is up by closer to 8 to 10 points in the national polls. Even if you assume that President Donald Trump gets the average bounce since 2004 and Biden gets no bounce, Trump won’t be close to the lead. The President needs something very different than usual to come out ahead after the conventions.

Second, the race for president this year has been incredibly stable. Biden’s lead has almost consistently been within a few points of 6 points. It’s never gotten higher than 10 points in the average and never below 4 points.

Stabler races tend to have smaller convention bounces. This could be part of the reason that convention bounces have gotten smaller in recent years.

View Trump and Biden head-to-head polling

If the last few months are any guide, we’re probably looking at an average convention bounce of less than 3 points in 2020.

Third, the conventions are likely not going to be the newsmakers they usually are. The conventions, themselves, are going to be incredibly scaled back. There won’t be the images of lots of people coming together in a crowded hall. Neither presidential nominee will be giving a speech in front of tens of thousands of the party faithful.

The broadcast networks, who the last couple of cycles were already only putting an hour of live coverage each night, will have even less to work with than normal.

The less coverage there is of the conventions, the less chance voters are going to have to discover something new about the candidates.

Indeed, part of the reasons conventions aren’t covered as much as they used to be is because voters already know a lot about the candidates. More voters hold a strong opinion of Trump at this point than any incumbent since at least 1980. More voters hold a strong opinion of Biden than any challenger since at least 1980.

Not surprisingly, convention bounces tend to be smaller when more voters hold strong opinions of the candidates.

Of course, we can’t take anything to the bank this year. Maybe more people will watch the conventions than normal because they’re stuck inside because of the coronavirus pandemic.

Still, the cumulative evidence suggests that a big convention bounce will be hard to come by this year.