WASHINGTON -- For Joe Biden, the Southern states that come after the earliest Democratic nominating contests are seen as something of a firewall. Even if the former vice president struggles early, primaries in states such as South Carolina, which follows close on the heels of New Hampshire, have sizable African-American populations and polls show those voters are firmly behind him.

Much of Biden’s advantage with black voters has been attributed to his time serving under President Barack Obama, the nation’s first black president, but a closer look at the data suggests there are deeper connections as well.

Biden’s Southern edge certainly looks formidable. In South Carolina, surveys consistently have Biden ahead by double-digits. And numbers merged from all of this year’s NBC News/Wall Street Journal polls show how strong Biden is with African-American Democratic primary voters.

Overall, Biden has largely maintained a decent edge with Democratic primary voters. He’s at 29 percent in the merged polls among all primary voters, while his next closest competitor Massachusetts Sen. Elizabeth Warren is 7 points behind at 22 percent. But Among African-American primary voters, the edge jumps to 38 points compared to his closest rival –- 50 percent for Biden to 12 percent for Warren.

That’s a massive margin with a group that is critical to any Democrat who wants the nomination. Exit polls in 2016 reported that African-Americans produced 61 percent of the primary vote in South Carolina, 71 percent in Mississippi and 51 percent in Georgia.

And the data show African-American voters stand out from the rest of the Democratic primary on a range of key factors -- factors that may push them toward Biden.

African-American Democratic primary voters also look different on age. They tend to be older than primary voters overall.

Consider that only 18 percent of the African-American primary vote sits in the 18- to 34-year-old age group. That’s 9 points lower than all other Democratic primary voters. Meanwhile, 57 percent of African-American primary voters are in the 50-and-older age group which is 6 points higher than other Democratic primary voters.

Older voters are generally less eager to embrace big changes.

And that leads to what may be the biggest difference between African-American primary voters and Democratic primary voters overall –- their ideology.

Among African-American primary voters, 61 percent label themselves as moderate or conservative. That’s 16 points higher than the rest of the Democratic primary electorate, whose moderate/conservative figure is 45 percent.

And, as you might expect, black Democratic primary voters are much less likely to say they are ideologically “liberal.” Only 34 percent of those voters use that word to describe themselves. Among other Democratic primary voters, the number is 20 points higher, 54 percent.

Older, more conservative voters? That sounds a lot like the voters Democrats are trying to win back in the industrial Midwest –- the kind of voters that many analysts think are drawn to Joe Biden and his working-class Pennsylvania roots. When you think of it that way, is it really a surprise that African-American primary voters lean toward Biden?

The primary season has not yet officially begun, and the coming year seems especially well-primed for a lot of twists and turns among the Democratic presidential field. Whoever wins Iowa and New Hampshire will undoubtedly have momentum when the primary contests turn south –- and momentum has a way of creating more momentum.

But Biden’s appeal in those Southern states shouldn’t be underestimated. He’s not just Barack Obama’s former vice president: On some key issues he may be the best fit for the African-American voters that will be crucial in those states.