The improvement has to do with the so-called enthusiasm gap. The dire predictions for the Democrats in November don’t necessarily assume a defection of voters from the Democratic Party to the GOP. Rather, Republican voters, riled up by being out of power, are more likely to turn out in the midterms; Democrats, resting on their laurels after the 2008 landslide, are much more likely to sit this one out.
A presidential visit to a toss-up race, according to Mellen, inspires some Democrats who would otherwise skip the polls to actually vote. Voter turnout always declines from presidential-year to midterm elections, but midterm toss-up races visited by the president see a lower decline in turnout than expected. Essentially, a visit from the president helps his party to narrow the enthusiasm gap that traditionally favors his opponents.
Not everyone is on board with Mellen’s findings. “It’s a stretch to say this factor is enough to keep the House Democratic,” says Larry Sabato of the University of Virginia. “Most models are suggesting a strong GOP victory.” Michael Lewis-Beck of the University of Iowa says “Visits seem to help little, if at all.” And Mellen will be the first to admit that his model isn’t rosy for Democrats: It still predicts they will drop 30-something seats.