Voters fill out their ballots on the first day of early voting Wednesday in Cincinnati. (John Minchillo/AP)

Over the weekend, The Washington Post released details from our most recent poll conducted with ABC News. One particular aspect of the poll speaks to the central question about what’s likely to happen in next month’s midterm elections.

What’s that question? Who turns out to vote. I know, I know; it’s hackneyed to point out that the election will come down to turnout. But in 2018, that’s more true than usual.

Midterms are generally lower-turnout elections, meaning that the electorate is more likely to be weighted toward voters who vote more often. That correlates with things such as home ownership (because you don’t need to re-register to vote after having moved), to age (because voting tends to be an established habit) and to income (which correlates with both of those things). Age and income also overlap with partisanship: Republicans are more likely to have higher numbers on both fronts and are more likely to vote in lower-turnout elections.

This year, though, frustration with President Trump has shown increased enthusiasm among demographic groups that are more likely to back Democratic candidates. If those voters surge to the polls, it could easily offset the existing Republican advantage. But, then, there’s an argument that, following the contentious confirmation fight over Supreme Court Justice Brett M. Kavanaugh, less-frequent Republican voters (including strong Trump supporters) are also motivated to go vote.

Our new poll looks at how various groups say they plan to vote — and how likely they say they are to do so.

Overall, the contrast between enthusiasm (the percentage of respondents who say they’re certain to vote) and how they plan to vote (the “generic ballot” question, asking about support for the Democratic and Republican candidate in the poll respondent’s local House race) looks like this.

(Philip Bump/The Washington Post)

A little more than 75 percent of voters say they’re certain to vote; they prefer Democratic to Republican candidates by 11 points.

One of the central divides of the election, driven by feelings about Trump, is gender. That shows up in our poll, too: Women are more likely to support Democrats than Republicans, though they’re only slightly more likely to say they’re certain to vote.

(Philip Bump/The Washington Post)

If we overlay party onto that, the picture gets more interesting. Democrats are strongly pro-Democrat and Republicans pro-Republican, as you’d expect. Among independents, respondents were more likely to support Democrats, especially among independent women, among whom the Democrats have a 33-point advantage.

(Philip Bump/The Washington Post)

But those independents are also less likely to say they are certain to vote.

That pattern is more dramatic when we break responses down by age.

(Philip Bump/The Washington Post)

The youngest voters are also those least likely to say they’re certain to vote.

It’s important to note that among both independents and younger voters, the percentage saying they’re absolutely certain to vote is up from October 2014. Among independents, the percentage saying they’re certain to vote is up from 59 percent four years ago to 72 percent now. Among those younger than 40, the percentage is up from 42 percent to 67 percent. That’s the silver lining, but there’s still a cloud.

There’s a similar increase among nonwhite voters, less than half of whom said they were certain to vote four years ago and 72 percent of whom now say they are.

(Philip Bump/The Washington Post)

(Note the party split by gender among whites. More on that below.)

Why that lower certainty among nonwhite and younger voters? In part, perhaps, because members of those groups are also less likely to say it makes a difference who controls Congress. A new Pew Research Center poll finds a 35-point gap between the oldest and youngest voters on that question and a 13-point gap between white and black Americans.

(Philip Bump/The Washington Post)

Notice that Pew also found less belief in the importance of the election among less-educated voters. Our poll saw that, too — but the electoral ramifications of that are less clear.

Among whites with a college degree, for example, certainty is near 90 percent. Among nonwhites with a degree, certainty is still higher than it is among whites without a degree.

(Philip Bump/The Washington Post)

That last figure is interesting. Whites without degrees (often older whites) are a central part of Trump’s base but express less certainty about voting than those with a degree.

Looking for a pat takeaway from this polling? It’s all going to come down to turnout. Feel free to quote us on that.