Midterm election forecasts by political scientists and economists are starting to roll out, and the picture is not pretty for the Democrats. This one by Emory University political scientist Alan I. Abramowitz writing for Larry Sabato’s Crystal Ball predicts a net loss of 37 Democratic House seats in November.

Abramowitz’s projections are based on four factors, including two that will likely continue to change between now and the election: the generic ballot (currently tied in Abramowitz’s model) and presidential approval (Obama +5 in Abramowitz’s model). The two other variables are already fixed (current number of GOP held seats and whether the president’s party is the same or different than the congressional majority).

Sabato’s own estimate is a little lower at a 27 net seat loss for the Democrats.

Columbia University political scientist Andrew Gelman reports on some other projections in a post title, “The Democrats are Gonna Get Hammered.”

A couple caveats concerning all these forecasts. First, despite the historical tendency for the president’s party to lose seats in midterm elections (the president’s party has lost 24 House seats on average since World War II), in two recent years (2002 and 1998) the party controlling the White House actually gained House seats. Yet that seems like a highly unlikely outcome given the current models.

Second, these projections will continue to change as political conditions evolve between now and November. The two key variables to watch: generic ballot and presidential approval.

Abramowitz underscores this point, demonstrating why, even if the environment for the Democrats improves, the president’s party faces a daunting November:

Even under what might be considered a best-case scenario for Democrats, if President Obama’s net approval rating were to improve from a +5 to a +20, and Democrats were to regain a 10 point lead on the generic ballot, Democrats would still be expected to lose about 20 seats in the House. On the other hand, under what might be considered a worst case scenario for Democrats, if President Obama’s net approval rating was to fall from a +5 to a -20 and Republicans were to gain a 10 point lead on the generic ballot, Democratic losses would be expected to reach 54 seats in the House. So while the national political environment will clearly have an impact on the outcome of the House elections, under any plausible set of circumstances Democrats are likely to lose a substantial number of seats in November due to structural features that are already set.

The political implications of this wide range of outcomes are critical. A 20-seat GOP gain means Democrats retain the majority and Republicans will control less than 200 votes in the House (218 needed for a majority). Under Abramowitz’s worst-case scenario for the Democrats, Republicans capture the majority with some votes to spare and Rep. John Boehner (R-OH) becomes the Speaker of the House.

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