Former vice president Joe Biden speaks at the NAACP's national convention on July 24 in Detroit. (Bill Pugliano/Getty Images)

Former vice president Joe Biden continues to lead the 2020 Democratic primary field, with the essential, squeeze-it-into-the-first-line-if-you-can caveat that it’s still awfully early and an awful lot of people haven’t yet made up their minds.

Even with that caveat, though, national polling doesn’t mean a whole lot in a process where states vote in clusters. States that vote early tend to have the effect of weeding out lower-tier candidates, reshuffling voter preferences up the chain. National polling gives us a sense of big-picture trends, but it can also obscure the way the race might shake out.

On Thursday, Monmouth University released new polling showing how the race is shaping up in one of those early primary states: South Carolina, which votes fourth. There, Biden has a wide advantage, leading the field by nearly 30 points. With the essential, squeeze-it-into-the-third-paragraph-if-you-can caveat that only five candidates are familiar enough to voters in the state that most voters have an opinion of them.

(Philip Bump/The Washington Post)

The important detail in Biden’s support, though, comes in the difference between white and black voters in the state. Biden gets a majority of the black vote at this point, a remarkable achievement in a field of 262 candidates. (That’s an estimate of the size of the field that will probably be correct by the time you read this.) Among white voters? His lead over Sen. Elizabeth Warren (D-Mass.) is within the margin of error.

(Philip Bump/The Washington Post)

That big advantage with black voters is important. We’ve written about it before, comparing Biden’s position now with Hillary Clinton’s in 2008. But it’s also important to look at that support in the context of Clinton’s position in 2016.

That year, Clinton’s primary opponent for the nomination was Sen. Bernie Sanders (I-Vt.). Very quickly, a dynamic emerged: Clinton did much better with black voters than Sanders; and Sanders ran about even with white voters. The result was that as states voted, the demographics of the states were important.

Iowa and New Hampshire, both heavily white states, voted first. Clinton and Sanders tied in Iowa, and Sanders rolled over Clinton in New Hampshire (thanks in part to its proximity to Vermont). Nevada, with a relatively small black population, was another near-tie.

Then came South Carolina, which Clinton won in a rout. It was also the state with the largest density of black voters to that point. By Super Tuesday, when there were a number of heavily black states voting, Clinton ran up a big delegate advantage that she would never relinquish. (The chart below shows only states in which exit polling was conducted.)

(Philip Bump/The Washington Post)

In the states above where the density of black voters was less than 10 percent, Clinton won 45 percent of the delegates. In states with black voter density greater than 10 percent, she won 67 percent of the delegates. And those states had a lot more delegates at stake — giving her the lead.

So, in the abstract, this would seem like good news for Biden: a big lead with black voters pushing him to the front of the pack, just as it did Clinton.

There are three problems Biden faces, however, that Clinton didn’t. (Even setting aside the essential, point-it-out-at-least-three-times caveat that the field is in so much flux.)

To illustrate the problem, we’ll look at polling conducted in early-voting states this month by CBS and YouGov. Across the polled states, Biden gets 41 percent of the vote from black voters, more than twice the next-closest candidate. Among white voters in those states, he trails Warren.

(Philip Bump/The Washington Post)

Notice the margins here, though. Clinton won the states identified above by an average of 69 points. Those are run-up-the-score margins in places with a lot of black voters. A 20-point advantage, like the one Biden has in the CBS-YouGov poll, isn’t bad — but it’s not dominant. That’s the first problem.

That poll used its results to project how the top Democratic candidates might do in delegate counting after the voting was over. Delegate tallies rely on complicated math that’s not worth getting into here (read up, if you wish), but the point is straightforward: Biden is projected to lead once delegates from California, Texas, New Hampshire, Iowa and South Carolina are counted.

(Philip Bump/The Washington Post)

Notice, though, that his margins are often subtle. South Carolina stands out as a big burst for Biden, a reflection of the numbers at the top of this article. In California, though, he gets only about 20 more delegates than Warren or that state’s senator Kamala D. Harris. In Texas, he fares a bit better, picking up 25 more delegates than Warren. The advantage in South Carolina is his largest, at 32.

This is only five states, though, including the megastate of California, which wasn’t in the mix in 2016. California essentially replaces Georgia on the Super Tuesday calendar — trading a heavily black state for a more diverse one. A more diverse one with way more delegates and a high-profile home-state candidate. That’s the second problem.

The third problem is already visible above. The breakdown of delegates in Texas, per that YouGov analysis, is as follows:

Candidate Delegates
Biden 92
Warren 67
O’Rourke 48
Sanders 18
Harris 3

It’s not a head-to-head contest in 2020. It’s a head-to-head-to-head-to-(repeat 200 times)-head contest. That means that the delegate totals aren’t divvied up between Clinton and Sanders but, instead, between whichever candidates hit the required baseline in voting. It’s harder to pull away in part because the field is so big in the first place.

As we like to point out, leading the pack isn’t a bad place to be, certainly. But Biden’s position in polls shows both his strength and some ways in which his path forward might be trickier than Clinton’s was three years ago — and it’s not like her path to the nomination wasn’t without potholes.

Oh, also? It’s early.