National conventions aren’t what they used to be. They have become highly choreographed and lacking in drama (though there was more drama than normal at both conventions this year).

But the conventions still serve vital purposes. They enable the two parties and their candidates to make their case directly to the American people in a setting glitzy enough to attract viewers. And they enable voters to discern, albeit not infallibly, differences in attitude, demeanor, and policy between the contestants for the presidency and their backers.

They also reveal what the two parties think they can sell to the American public. This year, Donald Trump clearly believes he can persuade America that the country is in huuuge trouble. President Obama and Hillary Clinton believe they can show that this is not the case, especially when it comes to the economy.

President Obama’s decent approval rating tends to support the Democrats’ wager. So does the consensus that the economy is performing more or less okay. Sure, large segments of the working class are suffering. But part of that cohort is African-American, and it won’t vote Republican. As for working class whites, there may not be enough of them to elect Trump.

But what if the economy has been slowing significantly during the past 12 months? In that case, levels of satisfaction will likely diminish during the summer and into the fall, and Trump’s wager might be the winning one.

New data confirms that the economy has indeed been slowing significantly. Ed Morrissey points to a report by the Bureau of Economic Analysis that estimates that gross domestic product (GDP) increased at an annualized rate of 1.2 percent in the second quarter of this year. In the second quarter of 2015, GDP grew at more than twice that rate.

Since then, we have experienced three straight quarters of declining growth. By the first quarter of this year, the growth rate was down to 0.8 percent.

The second quarter number thus represents a small improvement. But now that we’ve had three straight quarters of annualized growth of around 1 percent, I think it’s reasonable to fear that we’re in an economic slump.

The good news for Democrats is that the public doesn’t seem to fear this. Consumer spending, which accounts for 70 percent of economic activity, accelerated in the second quarter, growing at an annualized rate of 4.2 percent — well more than double the 1.6 percent rate in the first quarter. This amounted to the strongest surge for consumer spending since the final three months of 2014, according to the Associated Press.

If the consumer confidence that these numbers seem to reflect remains strong, the Democrats should benefit in November. But the underlying growth numbers suggest that the confidence is misplaced and thus might wane before very long.

In sum, both parties appear to have made reasonable wagers about the economy. That’s one reason why we may be in store for a close election.