https://www.nationalreview.com/corner/how-grim-is-the-outlook-for-incumbents-below-50-percent/
As Greg Corombos observed on Wednesday, we’ve reached that time of year when the moment many of us type the letter “R” in a web browser, we automatically load the URL for the RealClearPolitics list of the day’s latest polls.
But there’s a school of thought that argues that what polling aggregates really give us is a sense of the level of support the incumbent enjoys. Incumbency carries a lot of advantages in American politics — usually, strong name recognition, some degree of public application of what one has accomplished in office, and significant advantages in fundraising. Most years, between 91 and 98 percent of incumbents get reelected.
There’s a rule of thumb that an incumbent who is polling above 50 percent is safe, and an incumbent polling below 50 percent is in trouble. After all, the voters already know who the incumbent is and what they think of him. If they don’t like him, they’re usually, at minimum, looking for other options.
For what it’s worth, way back in 2010, Nate Silver argued that “the incumbent 50 percent rule” was an oversimplification. “It may be proper to focus more on the incumbent’s number than the opponent’s when evaluating such a poll — even though it is extremely improper to assume that the incumbent will not pick up any additional percentage of the vote.” But I think most of us can agree that an incumbent would rather be above 50 percent than below it, and the higher your support in late polling, the better your chance of reelection.