“Keep in mind, midterm elections are low turnout elections,” Bitecofer writes in a post for the Wason Center for Public Policy at Christopher Newport University in Virginia, where she is the assistant director. “And what drives turnout at the margins in off year and midterm elections is negative partisanship fueled by being locked out of power in Washington, particularly the big, white house at 1600 Pennsylvania Avenue.” It has happened in the last three midterm elections — in 2010 and 2014 to the Republicans’s benefit, and in 2006 to Democrats’ benefit.

She points to last year’s statewide elections in Virginia as another example of this dynamic. Many analysts predicted a narrow win for Ralph Northam, the Democratic candidate, based on pre-election polls. Bitecofer predicted a larger one, because she expected a turnout gap. Northam ended up winning easily, by almost 9 percentage points.

For this year’s midterms, the Democrats still hold about a 7-point lead in the national polls. Bitecofer expects that will translate into a larger advantage in the actual vote, and she forecasts that Democrats will flip more than the 24 seats they need to retake the House. Her article includes a rating — will flip, likely to flip, toss up, etc. — for each seat.

As for Trump’s approval rating, it remains an unimpressive 42 percent, according to FiveThirtyEight.

Obviously, Election Day is still more than four months away, and a lot could happen by then. I asked Bitecofer what she saw as the biggest risk facing the Democrats, and she replied by email:

“Biggest risk for Dems is poor strategic messaging. Only a Democrat would look at a polarizing POTUS who polls in the low 40s and decide not to make him a centerpiece of their messaging. Obama was actually popular when the Rs deployed that strategy in 2010 and 2014. You want to tap into that referendum effect as much as possible.”

Related: Greg Sargent of The Plum Line advises Democrats not to get too caught up in the debate over abolishing I.C.E., the immigration-enforcement agency. Instead, as the headline on his piece puts it: “Keep the focus on Trump’s cruelty and incompetence.”