The national constituencies of senators Elizabeth Warren and Bernie Sanders surely overlap. Photo: Andrew Harrer/Bloomberg via Getty Images

Recent Democratic presidential nominating contests have been relatively simple. The 2000 (Gore versus Bradley) and 2016 (Clinton versus Sanders) primary battles were almost entirely two-candidate affairs. 2008 quickly devolved to a two-candidate fight between Obama and Clinton by the end of January. The 2004 competition was all but over after John Kerry won both Iowa and New Hampshire, and among the viable candidates, only John Edwards lasted until March. There were all sorts of interesting fights underneath the surface in all of these contests, but nothing that required three-dimensional chess to understand. In most years, Establishment versus Insurgent was about as deep as you had to get.

The 2020 Democratic presidential race, however, is shaping up as a vast and complicated battleground with many viable and even more dark-horse candidates. Inevitably, both campaign operatives and political observers will have to analyze the field in terms of sub-contests between clusters of candidates pursuing particular constituencies. When Republicans had a similar situation in 2016, with 16 serious candidates in the fray, the metaphor of “lanes” in which such clusters competed for oxygen and viability before the deal went down became nearly ubiquitous. As early as March 2015 — before Donald Trump entered the race — the Washington Post’s Phillip Bump was slicing and dicing the field in terms of five “lanes” with different candidates competing for supremacy, with some transcending any one lane.

Bump had Scott Walker, Ted Cruz and Mike Huckabee as the leaders in the tea party lane; Walker, Huckabee and Jeb Bush as the top three in the “evangelical” lane; Bush and Chris Christie dominating the “moderate/establishment” lane; Walker and Bush doing best in the “very conservative” lane; and Rand Paul pretty much alone in a harder-to-discern “libertarian” lane.

Trump came along and scrambled these lanes and helped croak several candidacies. By February 2016, Morning Consult editor Reid Wilson posited just three lanes:

The five remaining candidates in the race are competing for constituencies who might conveniently be characterized as establishment voters, values voters and change voters.

Wilson suggested that Marco Rubio was fighting with John Kasich in the establishment lane; Ted Cruz was battling to subdue Ben Carson for supremacy among values voters; and Trump has the newly defined “change” lane to himself. Eventually, of course, all the “establishment” candidates vanished and Trump’s final battle was with Ted Cruz, who looked like an also-ran in the tea party lane in the early going. And in the end, the candidate who didn’t fit into any preexisting lane won the nomination and the presidency, casting doubt on the whole construction.

How might the chattering classes slice and dice the 2020 Democratic field? There are several ways to look at it:

1. Ideological lanes: Bernie Sanders will anchor the progressive lane, with potential competition from Elizabeth Warren, Tulsi Gabbard, Jeff Merkley and Sherrod Brown. If there’s a moderate lane, Joe Biden will be the pace-setter, with dark-horse House members John Delaney and Seth Moulton, former governor John Hickenlooper, and possibly Los Angeles Mayor Eric Garcetti, all following in his wake. Down the road, Amy Klobuchar and Beto O’Rourke might appeal to moderate voters and opinion-leaders if Biden doesn’t run or does poorly. Kirsten Gillibrand, Cory Booker, and Pete Buttigieg are hard to pigeonhole ideologically. They, along with O’Rourke, Warren, Klobuchar, and multiple dark-horses (including 2004 nominee John Kerry) have potential as “party unity” candidates — a lane that tends to form late in the nomination cycle.

2. Racial/ethnic/gender lanes: The size of the likely 2020 field means multiple candidates from demographic groups that are rarely represented in presidential contests. There’s never been a Democratic primary field with more than one viable woman or African-American. Gabbard, Gillibrand, Klobuchar, and Warren could create a “women’s lane” in theory. Booker and Harris could battle for African-American votes, beginning in the early South Carolina primary. Julián Castro and Garcetti could attract the attention of Latino voters. And although it’s a sentiment expressed more in private than in public, there’s a constituency for the idea that Democrats need a white male to beat Trump — especially someone who can appeal to Rust Belt white working-class voters. Joe Biden and Sherrod Brown could wind up competing in a white working-class lane of their own.

3. Generational lanes: Joe Biden, Bernie Sanders, Elizabeth Warren, Mike Bloomberg and John Kerry are all potential Democratic candidates who are (or in Warren’s case, will soon be) in their 70s. That makes virtually everyone else a possible “youth candidate.” Gabbard, Pete Buttigieg, and Calfornia congressman Eric Swalwell are in their thirties; Booker, Castro, Garcetti, and O’Rourke are in their 40s. If Alexandria Ocasio-Cortez had reached the constitutionally minimum age of 35, she might be a compelling candidate for the hard-to-mobilize, but sizable, millennial constituency.

4. Fame lanes: In a big field like 2020’s, less-well-known candidates will inevitably battle with each other for the media attention the celebrity candidates take for granted. In a social media era, fame can arrive quickly (as Ocasio-Cortez has demonstrated). So perhaps one or two of the candidates you have never heard of can strike name-ID gold before things get really serious.

5. The electability lane: Depending on all sorts of factors such as the objective condition of the country and Trump’s relative popularity, the Democratic nominating contest could revolve around evidence and impressions about various candidates’ ability to beat the incumbent. Several proto-candidates, including Biden, Brown and O’Rourke, have nascent “electability” arguments that could grow powerful if Democrats begin to worry the 2020 general election will be as close as the last one. General election trial heats testing this or that candidate against Trump could become important, despite the bad experience Democrats had with trusting 2016 polls showing Hillary Clinton handily beating the mogul. Very particular electoral college arguments for electability — e.g., Sherrod Brown’s popularity in Ohio — could matter in a close nomination race.

6. Luck lanes: The hardest thing to anticipate and adjust to are the fortuitous events that shake up nomination contests before and just after voters begin voting. If, for example, both Biden and Sanders — who lead most early polls — decide not to run, everything could change. The millstone Elizabeth Warren is trying to shrug off involving the essentially silly “issue” of her claimed Native American ancestry is an example of variables that are hard to calculate in advance. Whoever does best in critical moments of the nominating contest could rise to the top of the charts with a bullet. It’s impossible to know in advance.

And that’s the key thing to keep in mind when contemplating efforts to neatly classify the Democratic field. The one thing we should have learned from the 2016 GOP contest is that every rule can be broken. Going into that contest, political scientists had largely concluded that party elites pre-control presidential nominations. Trump blew up that supposition, which is part of the reason so many potential Democratic challengers to him are standing in line for 2020 in what some have labeled the “Why Not Me?” race. The primaries may surprise us, and there’s even a chance no one will have the nomination nailed down before Democrats gather for their convention in July. The “lanes” surviving candidates would traverse in the first truly deliberative Democratic convention since 1952 are impossible to anticipate. So perhaps we should treat it as a wide-open highway.