Recent special elections bode well for Democrats

If Republicans were about to experience a breakthrough among black voters, as some polls had suggested, New Jersey’s tenth congressional district (which includes Newark) might be a place to start. Around half its residents are black. But in the special election on September 18th to fill the district’s vacant House seat the Democratic candidate, LaMonica McIver, won in a landslide. She defeated her opponent by 81% to 16%—a larger margin than President Joe Biden managed there in 2020.

It is no shock that a Democrat won the deep-blue district. But the result is the latest in a string of strong scores for Democrats in special elections. This yardstick could endorse recent polls showing Vice-President Kamala Harris’s party taking the lead—or merely confirm the popularity of Democrats among the few motivated, hard-core voters who reliably show up for off-cycle elections.

In past presidential campaigns special elections have not carried much of a message about the contest at the top of the ticket (at least, none that could not anyway be gleaned from opinion polling). But in congressional elections, which have relatively few polls, the results can be revealing. In 17 elections to the House of Representatives since 1990, the party performing best in interim elections went on to win the popular vote 13 times (see chart). Moreover, special elections provide a valuable complement to polls, since they are unaffected by survey methods. Combining them with polls yields much more accurate predictions than either indicator does on its own.

This prognostic power is one reason why, for the 2022 elections to the House, The Economist predicted fewer Republican seats than some other forecasts did. Democrats faced an uphill battle to defend control of Congress. Though Mr Biden’s poor approval rating pointed to a “red wave” and polling suggested a narrow Republican victory, Democrats’ strong performances in special elections nudged our forecast towards a closer result. The Republicans won 222 seats, just four more than the minimum for a majority and far below expectations.

This year Democrats are doing even better in special elections. To estimate their performance, we compare both parties with a “benchmark” for each ballot, based on the most recent regularly scheduled election result for the same seat. In New Jersey’s tenth district Ms McIver outperformed her benchmark vote share by three percentage points. A moving average of these scores, with greater weight for federal than local elections, gives the Democrats a 3.3-point edge. Such an advantage will give the party a boost in our forthcoming forecast of the congressional elections.

There are reasons to be sceptical, however. In recent years the Democrats have found greater support among college-educated voters, who are more likely to turn out in off-cycle elections. In the general election the party will have no such advantage. This might explain why Democrats did worse in the general elections of 2020 and 2022 than you would expect from special elections alone. The Republican nominee, Donald Trump, has shown he can mobilise less engaged, non-college voters. These voters might not choose to turn out for an interim contest, but they are likely to support his congressional colleagues if he can coax them to the ballot box.

Although this dynamic complicates the picture, special-election results should still cheer Democrats. With less than six weeks left in the race, you would rather be the party winning landslides. ■

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