Heading into 2016, the Democrats held a slight lead in what’s called the “generic congressional vote”: Polling which asks people very simply who they plan to vote for in the next House race, the Democrat or the Republican. In mid-October, the Democrats held a six-point advantage, but that narrowed as Election Day approached, until the margin was under a point. The Republicans ended up getting more votes.

Pollsters are already asking the same question for 2018 — but the results are very different. In the past five results from live-caller polls, the results have been Democrats plus-13, Democrats plus-15, Democrats plus-11, Democrats plus-15 and Democrats plus-18. Those are from Marist, Monmouth, NBC-Wall Street Journal, Quinnipiac and CNN-SRSS.)

Tracking the average of polls on the question over the past two months (using data from RealClearPolitics) you can see the gap start to widen about 10 days ago — shortly before the Alabama special Senate election.

It’s not clear that the race in Alabama actually had an effect on these numbers. What we can do, though, is look at how the vote preference changed for demographic groups, using data from that CNN-SRSS poll released Wednesday.

The pollsters were direct about the scale of the Democratic advantage.

“Among registered voters,” CNN reports, “56% say they favor a Democrat in their congressional district, while 38% prefer a Republican. That 18-point edge is the widest Democrats have held in CNN polling on the 2018 contests, and the largest at this point in midterm election cycles dating back two decades.”

The last CNN poll on the question came in August. At that point, the Democrats had a 9-point advantage among registered voters, about the same as the advantage they enjoyed with that group in April. So what changed?

Here’s how various demographic groups have shifted in CNN’s three polls this year.

A lot of lines there, so let’s break some out.

Since August, four groups moved to the Democrats by at least eight percentage points on net. (That is, the margin by which they preferred one party to the other moved to the Democrats by that amount.)

  • Men (plus-12)
  • White people (plus-8)
  • 45 and older (plus-8)
  • Whites without college degrees (plus-10)

If you’re familiar with political demographics, you might recognize a pattern to those groups: They’re all groups which have been an important part of the Republican voting bloc, particularly recently. Whites without college degrees — a pillar of President Trump’s 2016 win — and older voters still prefer the Republican candidate. White voters, though, are split on the question, with 46 percent preferring the Democrat and 46 percent preferring the Republican. In April and August, the Republicans had an eight-point advantage with that group.

In the two previous polls, Republicans also had more support from men. In the most recent CNN poll, men prefer the Democratic candidate.

There are two gigantic caveats that should be noted.

The first is that the trend in CNN polling is one pollster and the shift is largely a change between two polls. Banking on those shifts explaining everything about the political moment is not recommended.

The second caveat is that we are still about 11 months away from the election. Less than a month before the 2016 election, as we noted above, the Republicans made up a six-point gap in the generic ballot. Over 11 months, they could certainly make a significant dent in this one.

In its analysis of its poll results, CNN notes that two-thirds of Americans are dissatisfied with how the nation is being governed — an attitude that would have worked to the Republicans’ advantage more in 2016 when they at least could blame Barack Obama for part of it. (In December 2015, three-quarters of Americans expressed dissatisfaction with the country’s governance.)

Now, it is very hard for the Republicans to argue that they don’t bear the blame if you don’t like how things are going. White people and men are more likely than nonwhites and women to say that they are satisfied with how the country is being governed — but still only about a third of those groups hold that opinion, according to CNN’s poll. It seems only logical, then, to assume that this may help explain why those voters have suddenly moved away from thinking they’d like to renew the Republican grip on Congress next year.