The conventional wisdom used to be that incumbents polling below 50 percent were in trouble because undecided voters broke heavily towards the challenger. Incumbents could only expect to receive roughly the same percentage on Election Day as their last poll number.
However, a comparison of recent polling with final results shows that incumbents having been routinely exceeding their final poll numbers by significant margins. This miscalculation made fools of Republican pundits in 2012 as they predicted a comfortable Romney victory. Complete reliance on the 50 percent rule even cost Dick Morris his job as a Fox News election analyst.
Given Congress’s historically low standing with the American people it does seem counter-intuitive that this would be the case. Conduct a man-on-the-street interview about Congressional Elections and you are likely to hear “vote the bums out.” Despite the tough talk, voters who remain undecided appear to like their incumbents.
Harry Reid, the most well known incumbent of the 2010 election, cleaned up the undecided vote as he finished five points above his final poll average. During the 2010 election, undecided voters sided with Senate incumbents in California, Colorado, Louisiana, New York, North Carolina, Oregon, and Washington. In Louisiana, David Vitter was running for re-election for the first time since his prostitution scandal. Vitter’s final number was nearly five points higher than his polling average.
In 2012 it was the challenger Mitt Romney who actually finished below his final poll number. All of the undecided voters and even some soft Romney voters apparently went to President Obama.
Obama was joined in exceeding his poll numbers by a number of other incumbents. Longtime Florida incumbent Bill Nelson exceeded his polling average by five percent and more than doubled his projected victory margin. Democrats in Missouri, Pennsylvania, Michigan, and New Jersey all exceeded their final poll average by at least five points and went on to win by much larger margins than projected.
Not a single Senate race in 2010 or 2012 saw a challenger come from behind on Election Day. In many cases, incumbents blew open moderately close races for double-digit victories. In a few instances such as Nevada and Colorado it was actually the trailing incumbents who came from behind to win.
The reason for incumbent success on Election Day may hinge on the undecided voters not actually showing up. A 48-45 incumbent lead with seven percent undecided, turns into a 52-48 incumbent win if those seven percent do not actually vote. As many surveys push leaning poll respondents to choose between candidates, those poll respondents who are still undecided after being prodded may very well not vote on Election Day. Not only may undecided voters be staying home or siding with incumbents, but the numbers suggests that soft supporters of the challengers may also end up supporting the incumbent.
It is also worth noting that many of the incumbents who have performed better on Election Day are Democrats, and Democrats have consistently performed better than their polling over the past few cycles. The strong Obama turnouts of 2008 and 2012 may account for a good deal of the Democratic incumbency strength, but 2010 was a very good Republican year in which Democratic incumbents still did well.
Another advantage for incumbents is their ability to build their get-out-the-vote networks while in office. Harry Reid squeezed every last vote out of Democrats in Nevada while his challenger struggled with her ground game. This advantage may vary depending on the political experience of the challenger.
The Election Day incumbency edge should worry Republicans as they need to defeat at least two Democratic incumbents to retake the Senate majority (Montana, West Virginia, South Dakota, and Iowa are all open seats). In Arkansas, Louisiana, and Alaska, Republican challengers have the advantage of running in bright red states, but they also face incumbents who have deep family ties in their respective states.
Democrats have a very strong ground games in Colorado and Iowa, which also should give the GOP pause (in addition to the new voting rules in Colorado).
While Republicans have a clear edge in Senate polls, a one or two point poll advantage may not be enough to translate into victory on Election Day. The GOP needs to anticipate Democratic incumbents outperforming the polls by two or three points in each race or risk a disappointing Election Night.