Sen. Bernie Sanders (I-Vt.) came much closer to winning the 2016 Democratic presidential nomination than anyone would have expected at the beginning of that campaign. Despite how he presented his position early in 2016, he was never really likely to win the nomination after Hillary Clinton built a large delegate advantage in (mostly) Southern primaries. But that he would at some point poll about evenly with Clinton — within a point in the RealClearPolitics polling average in mid-April — was itself a shock.

It set some expectations for his 2020 bid. Wouldn’t the candidate who at one point earned the support of more than 46 percent of the Democratic primary electorate in 2016 be well positioned four years later? Particularly given the size of the field, locking down a big chunk of the electorate could be a huge advantage.

Polling of the 2020 race has indeed shown remarkably stability in Sanders’s numbers, as one might expect from someone with an enduring base — but not particularly strong support. Sanders’s standing in the polls has ranged over only 10 percentage points in the RealClearPolitics average, a smaller range than any of the five candidates who at some point hit at least 10 percent in that average.

On 70 percent of days over the past year, Sanders’s poll average has been between 15 and 18 percent.

The question, then, is who that 15 to 18 percent of the electorate is. Which groups have stuck with Sanders four years after his first bid?

To answer that question, we pulled Washington Post-ABC News polling from September 2015 (when he was still a long shot), March 2016 (when he was closing in on Clinton) and our poll released in early November. We have comparable data for a number of demographic groups, including age, gender, ideology, race, education and income.

Here’s support for Sanders by demographic in all three polls. The numbers show the change in support from the group from the 2015 or 2016 poll until the one released last month. What we’re looking for are places where support dropped a lot — or not much at all.

Almost uniformly, the drops from the March 2016 poll are dramatically larger than the drops from the September 2015 poll, a reflection of the surge Sanders saw as he became the sole viable alternative to Clinton. It suggests, though, that his support at that point was largely a function of his position in the race; that they didn’t become part of his political base.

Two demographic groups in particular stand out. One is nonwhite Democratic voters, a group that was a significant factor in his 2016 loss. Sanders’s support in primaries correlated inversely to the density of black voters, and Clinton’s delegate lead was largely a function of her dominating in heavily black states. In our November poll, he does 9 points better with nonwhites than he did four years earlier. Important caveat: The margin of sampling error for the group is 8.5 percent, so this may just be noise.

The other group that sticks out is whites with a college degree. Sanders’s support with that group dropped significantly from September 2015 until now. (It’s probably a big reason his support with whites overall similarly dropped.) Back then, Sanders did much better with whites without a degree than with those who had a degree, in part because his support has consistently skewed younger. (Note that his support among younger voters is now about what it was in September 2015, while his support with people over 50 has dropped.)

In our November poll, we see where those whites with college degrees went: to Sen. Elizabeth Warren (D-Mass.). Those 50 and over went to former vice president Joe Biden.

Of course, Sanders still leads with young people, if we consider people under 50 as uniformly “young.” (We should, in my humble, not-old opinion.) There are four groups where Sanders earned more than 20 percent support both four years ago and in November: people under 50, men, those making less than $50,000 a year and liberals. However, his support among liberals dropped 7 points (within the margin of error). Warren led with that group in our most recent poll.

In other words, Sanders’s base now appears to be mostly what it was four years ago, with the exception of college-educated whites. That group, of course, is central to the candidacy of a Democrat who was barely known four years ago: Pete Buttigieg, the mayor of South Bend, Ind.

Take Buttigieg and Warren out of the race, and it would be interesting to see where Sanders lands. Perhaps the most likely place? In a one-on-one contest against a more moderate Democrat with strong black support.

In other words, he’d end up in familiar territory.