If I had to pick one word to describe the Democratic presidential primary, it would be “fluid.” The field of candidates is sprawling, and almost a year remains before the first nominating contest. In primaries, voters are more prone to changing their minds than they are in general elections, so Democratic voters’ preferences will likely change several times between now and next spring.

It can therefore be useful in early polls to know not only which candidate is a voter’s first choice, but also who her backup is. In its weekly tracking poll of the 2020 Democratic presidential field, the pollster Morning Consult has been asking voters just that. And while the results might not be too surprising — former Vice President Joe Biden or Sen. Bernie Sanders are consistently voters’ second choices, just like they are voters’ first choices in almost every other national poll — they do highlight the limitations in how the media (including FiveThirtyEight) analyzes presidential primaries. Namely, the blocs/corners/lanes/circles we try to fit candidates and voters into are a lot messier in real life than we sometimes imagine.

A look at voters’ second choice picks The second choices of Democratic primary voters, broken down by their first-choice candidates, according to a Feb. 18-24 Morning Consult poll First choice second choice Biden Sanders Harris Warren O’Rourke Booker Klobuchar Biden 26% 19% 17% 20% 20% 15% Sanders 28% 15 24 22 16 15 Harris 12 7 13 12 17 12 Warren 8 16 14 8 8 12 O’Rourke 8 6 11 7 10 8 Booker 6 4 11 5 8 6 Klobuchar 3 2 6 4 4 3 Sample sizes for each first-choice candidate, among registered voters: Biden — 4,546; Sanders — 4,215; Harris — 1,583; Warren — 1,111; O’Rourke — 1,057; Booker — 577; Klobuchar — 530. Source: Morning Consult

The first lesson from this table is that early primary polls are, in large part, driven by name recognition. At this stage, voters may have only heard of a few of these candidates, and chances are two of them are Biden and Sanders (who are the two best-known candidates in the field). So of course they are a respondent’s second or third choice (if not his first).

The second lesson is that “lane” analysis, or the idea that candidates are competing for support within different wings of the party (e.g., the “establishment lane”), can be overrated. This isn’t meant as shade — FiveThirtyEight has classified its own wings of the party, too. It’s just important to remember that this kind of analysis has its flaws and limitations, particularly this early out. Other than both being white men, Biden and Sanders are about as different as Democrats in 2020 can get: one is establishment to the bone with a less-than-purely liberal record, while the other is a grassroots-backed insurgent who identifies as a socialist. And yet more than a quarter of Biden supporters say Sanders is their second choice, and more than a quarter of Sanders supporters say Biden is their second choice.

Now, don’t get me wrong — there is some interesting variation in the second-choice vote shares that jibes with sorting candidates into “lanes.” To take one example, Sanders ranks as the preferred second choice of supporters of Sen. Elizabeth Warren, whose progressive economic message dovetails with Sanders’s. To take another, Sen. Kamala Harris ranks higher among Sen. Cory Booker supporters than she does among any other candidate’s supporters, and Booker likewise does better among Harris supporters than he does any other bloc. That supports the idea that Harris and Booker, as the race’s two most prominent African-American candidates, might appeal to similar bases.

But it’s less variation than I think most people would expect, and there are clearly large chunks of voters who are perfectly willing to vote for a candidate in a different lane. As political scientist David A. Hopkins of Boston College recently pointed out, voters simply aren’t so well informed or calculating to split candidates cleanly into such factions. What’s more, lanes haven’t accurately predicted how previous presidential nominating contests would shake out after candidates began withdrawing and support started shuffling around. Current events and the shifting media spotlight after candidates win or outperform expectations in early primary states can also shake up fields, and candidates’ own marketing efforts can often succeed at winning over voters that may not be part of their “natural constituency.” Voters may use ideology and identity as a guide, but “lanes” are hardly an ironclad theory. Frankly, primaries are unpredictable — maybe we should all just get more comfortable with that idea.





FiveThirtyEight’s 2020 draft: Episode 2