Most of us treat “incumbency advantage” as axiomatic.
Incumbents, particularly in the House, generate significant advantages over challengers by using the perks of office to increase their name recognition and develop a positive image.
It certainly sounds plausible. After all, more than 90 percent of House incumbents who seek reelection win their races.
Reelection rates ebb and flow, but only a little.
In 1970 and 2010, they “fell”— to 85 percent. In 2012, it was 90 percent, and in 2008 it was 94 percent.
But reelection rates are not, in and of themselves, evidence of an advantage conferred by virtue of incumbency and the tools it provides.
For example, if Democrats won Democratic districts and Republicans won Republican districts, you would see these same reelection rates: partisanship, not incumbency advantage, would be the cause.
Similarly, it is possible that members win elections in the first place because they are superior candidates and their reelection is just further evidence of their campaign prowess.
Many outstanding scholars have labored in this vineyard and provide only somewhat different results.
Most find a real incumbency advantage after controlling for other factors and estimate the size of the effect at 8 to 15 points at its peak. Most see the peak coming in the 1970s-1990s eras.
One other critical point of consensus emerges. Despite high reelection rates, in recent years the incumbency advantage has declined sharply: by 50 percent or more in most estimates.
Professor Gary Jacobson of the University of California, San Diego, for example, finds the incumbency advantage reaching a high of 15.4 points in 1986 and 1988.
By 2012, it had plummeted to less than 5 points — a decline of two-thirds.
Professors Andrew Gelman and Gary King used another calculation that put the advantage at a high of 12.3 points in 1986, which declined to 5.2 points in 2010.
Professor Robert Erikson of Columbia finds incumbency advantage falling from a high of about 8 points to about 2 today.
Two culprits seem to bear the blame in the case of the vanishing incumbency advantage (to play off the title of perhaps the most famous paper ever written on congressional elections, “The Case of the Vanishing Marginals” by one of my former teachers, professor David Mayhew, who was honored at a conference last week): partisanship and money.
As suggested above, rising partisanship can account for high reelection rates as long as Democrats are mostly elected in Democratic districts and Republicans in GOP districts.
That is exactly what has happened.
As Jacobson points out, the correlation between presidential and House votes in congressional districts has risen from 0.54 in 1972 to 0.95 in 2012.
That is, more than 90 percent of the variation in House vote can be explained by presidential vote.
And presidential vote, too, is driven by underlying party identification.
With partisanship ruling the roost, there is little room for members to carve out their own image and create a personal vote separate and apart from the partisan leaning of their district. It does happen, but it’s rare.
Money contributes to its rarity. Between 1986 and 2010, the cost of winning a House seat more than doubled in real terms.
That additional money means that no strong positive goes unstated, and no flaw goes unreported. The dollar value of the advantages conferred by incumbency is dwarfed by the impact of the vast spending.
None of this suggests that incumbents should stop giving speeches or sending newsletters, only that the advantage these tools once provided has greatly diminished.
Mellman is president of The Mellman Group and has worked for Democratic candidates and causes since 1982. Current clients include the Majority Leader of the Senate and the Democratic Whip in the House.