(CNN) House forecast: Democrats will win 226 seats (and the House majority) while Republicans will win just 209 seats. A Democratic win of 202 seats and 260 seats is within the margin of error.

If Democrats win the House, as we currently forecast, it will be because of women voters. The Democratic Party is currently benefiting from the largest gender gap on record for a midterm election.

In an average of the last five live interview generic congressional ballot polls , Democrats hold a substantial 22-point lead among women voters. That compares with a Republican advantage of 8 points among men voters. In other words, if only men were voting in this election, Republicans would not only hold onto their House majority, they would be expanding it.

The previous record high was 21 points in 2014. The 30-point gap in 2018 is 19 points higher than the average since the 1980s (when the gender gap first began to appear).

The gap seems to be driven by women's move to the left. By my calculations, there has never been a midterm in modern history in which women voted for Democratic candidates by more than 17 points. The current polling average suggests a margin of 5 points greater than that.

Key to the current polling position of Democrats is that they are expanding upon the advantage that Hillary Clinton had with women in 2016. Whether you look at the exit polls or the Pew Research Center's study of validated voters, Democrats in 2018 are doing anywhere from 7 to 9-points better among women than Clinton did.

Even better for Democrats is that if you had to choose between doing well with men or women, you'd prefer to do well with women voters. They make up a larger share of the electorate. Historically that hasn't meant much because the gender gap has been relatively small. The gap is becoming large enough this year that it could be worth 1 to 2 points to the Democratic margin. That may be what puts Democrats over the top, if they do indeed win the House majority.

The other part of why the gender gap is working in the Democrats favor is that Republicans are simply not doing well enough among men. Donald Trump won men by 11 points in 2016. To counteract the Democrats larger advantage with women, Republicans would need to be doing better than they did two years ago. The average poll does have them ahead, but by 3 points less than in 2016.

The 30-point gap between how men and women are voting is astounding, not just for historic nature (more on that in a minute), but for the fact that it seems to be holding or even expanding. When I looked at the gender gap in the early summer, it stood at 26 points. With just a few weeks until Election Day, it seems unlikely that the gap will shrink greatly.

It's also consistently shown up in every live interview poll. Sometimes when a trend appears in an average, it widely varies between polls. Not so here. In each of the last five polls, Republicans always lead among men. Democrats always lead among women. In all five, the gender gap is 24 points or greater. Put another way, even the pollsters that have the smallest gaps still show a historically large one.

Of course, a gender gap doesn't guarantee Democratic success. If the polls are underestimating Republican strength among men and women, the gender gap may be as large as ever and Republicans may hold onto the House.

For now, the gender gap looks like it will power Democrats to a midterm victory.