Vice President Biden and former secretary of state Hillary Rodham Clinton appear onstage at the Vital Voices Global Partnership 2013 Global Leadership Awards gala at the Kennedy Center on April 2, 2013. (Cliff Owen/AP)

In Atlanta on Friday morning, Vice President Biden confirmed for the first time that he’s seriously considering making a bid for the presidency in 2016. His entry would instantly scramble the race.

Polling averages show Biden as currently the first choice of about 15 percent of Democratic voters, and it’s likely that this number would climb higher following an official announcement of his candidacy.

Which of the current contenders for the Democratic nomination has the most to lose from a Biden run? Front-runner Hillary Clinton and her main rival for the nomination, Sen. Bernie Sanders of Vermont, could both conceivably find their supporters defecting to the vice president.

(The three other candidates in the race—Lincoln Chaffee, Martin O’Malley and Jim Webb—are polling at such low levels right now that it’s hard to say much about the votes they might lose to Biden.)

To the extent that Sanders is relying upon “anybody but Hillary” voters for his support, an entry by Biden — who would be a much better-known alternative to Clinton — could cause Sanders’s poll numbers to decline.

On the other hand, it’s hard to find much daylight between Biden and Clinton with regard to policy. Thus, it’s possible that Biden would be appealing to current Clinton supporters who like her views but feel uncomfortable with her weaknesses as a candidate.

We can get a sense of which of these two scenarios might unfold thanks to some interesting variation in how polling on the Democratic race has been conducted so far. Of the 56 national Democratic primary polls conducted since the beginning of May, 45 of them have listed Biden as a candidate while 11 have not.

This presents a simple way to forecast how a Biden entry would affect Clinton and Sanders: by comparing their numbers in surveys that list Biden as a choice and those that don’t. A candidate whose support is substantially lower in surveys that include Biden could reasonably be expected to be hurt more by his entry than one whose numbers remain steady.


The chart above suggests that a Biden candidacy would be substantially worse for Clinton than Sanders. Over the past four months, Clinton has consistently polled lower in surveys in which Biden is included as a choice. A simple statistical analysis controlling for time trends (not shown here) estimates that Clinton performs about six percentage points worse in these polls. By contrast, Sanders’s numbers are affected not at all: they’re essentially the same whether or not Biden appears on the ballot of candidates offered to survey respondents.

To be sure, certain pollsters have consistently included Biden and others haven’t. Thus it’s conceivable that the graph merely reflects “house effects” — persistent biases for one candidate or another that are associated with a particular polling firm. However, I think it’s unlikely that house effects would produce the pattern found here.

In public, Clinton and her campaign have welcomed the notion of Biden jumping into the ring with confidence and graciousness. But in private, they’ve made moves to discourage his candidacy and to keep her supporters from from defecting.

The numbers here help to explain why: Clinton has much more to lose from a run by Biden than any of her rivals for the Democratic nomination.