Dave Wasserman, the Cook Political Report's House analyst, says the most under-covered aspect of 2018 is that "a blue wave is obscuring a red exodus." Republican House members are retiring at a startling clip — a trend that senior White House adviser Kellyanne Conway told me earlier this year was worrying her more than any other trend affecting the midterms.

What's happening: There are 43 Republican seats now without an incumbent on the ballot. That's more than one out of every six Republicans in the House — a record in at least a century, Wasserman says.

Why this matters: Just in the past eight months, the number of vulnerable Republican seats has almost doubled, according to Wasserman. Democrats need to win 23 seats to claim control of the House. Today, the Cook Political Report rates 37 Republican-held seats as toss-ups or worse. At the beginning of the year, it was only 20.

The big picture: Wasserman says the most important sign that 2018 will be a "wave" year — with Democrats winning control of the House — is the intensity gap between the two parties. In polls, Democrats consistently rate their interest in voting as significantly higher than Republicans. And Democrats have voted in extraordinary numbers in the special elections held the past year, despite Republicans holding on to win almost all of these races.

"There's a bit of over-caution, perhaps, on the part of the punditocracy, after what happened in 2016," Wasserman told Axios. "But if anything most media could be under-rating Democrats' potential to gain a lot of seats. They could be caught being cautious in the wrong direction."

Wasserman has a vivid way of describing the most harmful dynamic for Republicans in November. "This election is the year of the angry female college graduate," he said.

"The most telling number in the most recent NBC/WSJ poll is that Trump's approval rating among women with college degrees was 26 percent. That's absolutely awful and the intensity of that group is extraordinary. They're already the most likely demographic to turn out to vote in midterms. But never have they been this fervently anti-Republican."

"In 2010 when Republicans won back control of the House, I would argue that was the year of the angry white senior ... and yes, there was a lot of consternation and upset about Obamacare."

"But the main reason for that was who wasn't voting. It was the young, and non-white Obama surge voter from 2008, who stayed home, and it lost Democrats the election in 2010."

The bottom line: "Yes, it's about how upset suburban professional women are, with regard to family separations at the border and Trump's temperament and behavior. But it's also about who's not voting. And that's primarily men without college degrees who are Trump true believers."