A few months ago, a Democrat who is personally involved in the presidential race was offering his private analysis of the competition. He framed it in a way that was different from the conventional assessment but that might prove to be a smart way of thinking about what is beginning to unfold.

At the time, former vice president Joe Biden’s performance on the trail and in debates was raising doubts about his candidacy. But this Democrat, who only wanted to assess the race without being identified, said he remained reasonably bullish about Biden’s chances.

The reason, he said, is that he saw the competition for the nomination coming down to a contest between the progressive wing of the party and the African American wing. He believed that Biden’s support in the black community could be the crucial difference in the outcome of the race.

That formulation is a variation of the way the Democratic contest is often framed, as the progressive wing vs. the moderate wing. But today it seems all the more relevant, given two polls released this weekend.

The latest Iowa poll conducted by J. Ann Selzer for the Des Moines Register and CNN, published Friday evening, shows Sen. Bernie Sanders (I-Vt.) now leading there with 20 percent support, followed by Sen. Elizabeth Warren (D-Mass.) at 17 percent, former South Bend, Ind., mayor Pete Buttigieg at 16 percent and Biden at 15 percent.

That represented growth for Sanders, who was at 15 percent in November, and a decline for Buttigieg, who led the November Iowa poll with 25 percent support. Warren was up a single point, while Biden’s position in the Iowa poll was unchanged between November and today.

The Iowa poll matched what is visible on the ground in Iowa, which is that Sanders, after a heart attack last fall and other setbacks to his campaign, is on the move. His supporters in Iowa, as elsewhere, are loyal and committed. His campaign team believes his organization will be as effective as any other in getting people to the caucuses on Feb. 3.

But the Iowa poll also highlights an ever-changing landscape: In the four Register-CNN polls, there have been four different leaders: Biden, then Warren, then Buttigieg and now Sanders. Only 40 percent of Iowans in the new poll say they have made up their minds. The others are leaning toward someone but could be persuaded to change or haven’t picked anyone yet.

A Sanders victory in Iowa would give him a boost in New Hampshire, a state he won easily in 2016 but that also features a four-way competition a month ahead of its primary. Along with Warren, Sanders represents the strength and the aspirations of a progressive wing of the party heading toward the first votes of the year.

Based on the current numbers, Biden could finish anywhere in the top four in Iowa. He has thrown considerable resources, surrogates and personal time into the state in the past six weeks. The lack of movement should be a cause for concern. Because there appears to be more enthusiasm behind other candidates, Biden’s organization will have to push hard on caucus night.

The other poll tells the other side of the story. This one was conducted by The Washington Post along with Ipsos, a nonpartisan research firm and released Saturday morning. The survey sampled attitudes of 1,088 non-Hispanic black adults nationally from a large online panel recruited through random sampling of U.S. households. It represents one of the most extensive surveys of African American attitudes about the 2020 campaign.

One way of thinking about the Iowa poll is that the leading progressive candidates account for 37 percent of the vote today while the three leading moderate candidates, Biden, Buttigieg and Sen. Amy Klobuchar (D-Minn.), who is at 6 percent, also account for 37 percent. In other words, parity along the ideological scale.

But when the race is viewed through the prism of the African American vote, it’s a different story. Among black Democrats, Biden stands at 48 percent. Sanders is running second at 20 percent. Warren gets 9 percent and Buttigieg 2 percent. Biden has slightly more support than Sanders, Warren, Buttigieg, former New York mayor Mike Bloomberg, Sen. Cory Booker (D-N.J.), Andrew Yang and Tom Steyer combined.

In the survey of African American Democrats, Biden leads among men and women, liberals and moderates, and all educational groups. He leads in the states that will vote between now and Super Tuesday (March 3) and in the states that come after that. He leads in all regions, with his biggest support in the South.

The one group of African Americans where Biden doesn’t lead is among those under age 35. Sanders has the support of 42 percent of those younger African Americans, while Biden is at 30 percent. His deficit to Sanders among younger black Democrats is more than offset by his 60-point lead among those over age 65.

Another group is more closely divided. These are black Democrats who prefer a candidate who is closer to them on the issues. Biden has a statistically insignificant lead among that group. Among the much larger group who say the most important thing they want is a candidate who can defeat President Trump, a majority currently support Biden with everyone else in mid-double or single digits.

Describing the Democratic campaign as a competition between the progressive wing and the African American wing is, admittedly, something of an apples and oranges comparison. But it speaks to what remains one of the biggest unanswered questions of the 2020 Democratic nomination contest: Will African Americans stick with Biden if he stumbles in the first two states?

Should Biden do badly in Iowa and New Hampshire, that question would be answered in South Carolina, the fourth of the four early states to hold contests. As in the Post-Ipsos national poll, surveys in South Carolina have consistently shown Biden ahead, thanks primarily to his solid support among African Americans. There’s no reliable guide to the solidity of that support.

The Post-Ipsos poll provides good news for Biden, but like so much else thus far in the Democratic race, it captures impressions and attitudes amid a fluid contest and major news breaking on multiple fronts. African Americans remain a foundational part of the Biden candidacy. He cannot afford to see that foundation eroded by signs of weakness once the voters start to cast their ballots.