Biden is rising. But Sanders has a hidden edge today.

The groups that have most favored the senator from Vermont in the Democratic presidential race are much more widely distributed than the groups that have resisted him across the 14 states that will vote on Super Tuesday, an exclusive congressional district by district analysis has found.

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Latinos and non-college-educated whites, who have tilted solidly toward Sanders, constitute a critical mass of the eligible voting age population in a much wider range of districts than, college-educated whites and African Americans, who have been more skeptical of him, according to the analysis of census data by the University of Southern California Program for Environmental and Regional Equity provided to CNN.

Sanders is facing new headwinds this week, as a procession of party leaders have endorsed former Vice President Joe Biden following his commanding victory Saturday in South Carolina; that list includes former Senate Majority Leader Harry Reid, former Virginia Gov. Terry McAuliffe, former Rep. Beto O'Rourke of Texas, and former South Bend, Indiana, Mayor Pete Buttigieg and Sen. Amy Klobuchar of Minnesota, both of whom endorsed Biden on Monday after quitting the race in the last 48 hours. But this demographic pattern could help Sanders reach the threshold for acquiring delegates in a wider range of districts than any of his rivals on Tuesday and reinforce his status as the front-runner in the contest, even after Biden's recovery in South Carolina and the consolidation behind him by many party leaders.

In almost all states, Democrats distribute delegates to the party convention in July based on the results in individual congressional districts as well as the statewide totals; candidates need to reach a threshold of 15% of the vote in either to obtain any pledged delegates.

In all, the 14 states voting today -- from North Carolina, Virginia and Alabama in the Southeast to Texas and California in the Southwest -- house 169 congressional districts. Beyond the competition for the delegates and momentum that come from statewide victories, the candidates in effect are conducting 169 separate elections today as they compete for delegates on a district-by-district basis. (In Texas, the delegates are awarded by state Senate districts, but the distributions of the different demographic groups across them are similar.) Campaigns must target their efforts "not just state by state," Jeff Weaver, a senior adviser to Sanders, told me recently. "It is congressional district by congressional district. Particularly on Super Tuesday, we are looking at it as CD by CD."

To understand the demographic composition of this sprawling battlefield, Justin Scoggins, the data manager for the USC program, analyzed individual responses to the census' 2018 American Community Survey and then applied a data tool from Missouri Census Data Center to assign those individuals to specific congressional districts. That allowed him to calculate the demographic characteristics of the eligible voting-age citizens in individual congressional districts with greater detail than is usually available.

The results of the USC analysis underscore why Sanders could be positioned to deliver a very strong performance today, if Biden's resounding victory in South Carolina, and the cascade of endorsements that followed on Monday, does not dislodge the demographic patterns of support for the candidates from the first four contests.

Sanders has won a plurality of white voters without college degrees in each of the first states that have voted, according to election day surveys conducted by Edison Research for a consortium of media organizations including CNN. Sanders' advantage over Biden among those blue-collar whites has reached as high as 21 percentage points in New Hampshire and Nevada, though the former vice president closed the gap to just 5 points in South Carolina on Saturday, according to the exit poll.

Targeting Trump voters

The USC analysis shows how important it is for Biden to continue shaving Sanders' advantage with that group. Whites without college degrees represent one-third or more of the eligible voting-age population in 100 of the 169 House districts voting on Super Tuesday; they compose 25% to 33% in another 25 of the districts, the USC analysis found. In all, that means they constitute at least 25% of eligible voters in nearly three-fourths of all the districts voting today.

Manuel Pastor, a USC professor of sociology who's the director of the Program for Environmental and Regional Equity, says Sanders' connection with young voters has somewhat obscured his success at targeting some of the same working-class whites who were drawn to Trump's promises of political disruption.

"What doesn't get lifted up enough is Sanders' strength with the non-college-educated voters," said Pastor, author of the recent book "State of Resistance," which covers the Democratic rise to dominance in California. "What Bernie is trying to do is reach to that same disaffected group of workers but continually couch it in a rhetoric of not blaming the other, trying to resist scapegoating, and target the billionaires. Whether or not this is going to be enough to win across the nation in a general election, particularly when there is opposition research brought to bear later on, is still up to debate. But [in the primary] he is running very well among a traditional Democratic demographic."

By contrast, whites holding at least four-year college degrees, who have displayed considerably more resistance to Sanders so far, are not distributed nearly as broadly across the Super Tuesday states.

Those college-plus whites represent a third or more of the eligible voters in just 21 of the 169 districts voting today, and 25% to 33% in another 40 of them. That means they constitute at least 25% of eligible voters in only a little over a third of the districts.

That helps Sanders, because those well-educated voters have been among the Democratic constituencies most dubious of him. The senator did win them in Nevada, according to the entrance poll, but with only about one-fourth of their votes; he hasn't exceeded 21% of the vote among them in any of the other three states.

Just as the non-college whites more favorable to Sanders are distributed more broadly on Super Tuesday than the college whites dubious of him, the senator will benefit from a similar pattern among minorities. Latino voters, who have preferred him so far, constitute a critical mass of population across a broader number of districts in the Southwest battlegrounds of California and Texas than African Americans, the foundation of Biden's candidacy, do in the Southeast battlegrounds voting today.

As I've written, the period from late February through mid-March is the moment of maximum Latino influence on the Democratic nominating process. That influence peaks on Super Tuesday.

The USC analysis found that Latinos constitute one-third or more of the eligible voting-age population in 34 districts voting today, all of them in California and Texas; they also represent one-fourth to one-third of eligible voters in another dozen districts, again all in those two mega-states. In sum, Latinos constitute at least one-fourth of the eligible voters in about one-fourth of all the districts voting on Super Tuesday and more than half of the districts in California and Texas combined. And although the concentration isn't as great, Latinos also represent one-sixth to about one-fifth of the eligible voters in four of the seven districts in Colorado, which also votes today.

That's all good news for Sanders, because the evidence indicates he has substantially expanded his support among Latinos from 2016, when Hillary Clinton carried about three-fifths of them, according to a CNN analysis of all the exit polls conducted that year. This year, he posted a commanding lead among Latinos in the Nevada entrance poll and polls have shown him leading among them as well in California and Texas.

Challenging Sanders

By contrast, African Americans represent a critical mass of the population in a much smaller number of congressional seats. Blacks constitute one-third or more of eligible voters in just 10 districts across Super Tuesday, comprising three in Texas, two in Alabama, two in Virginia, two in North Carolina and one in Tennessee. They reach 25% in just two other districts. In California, black voters represent at least 25% of the eligible voting population in just the South Central Los Angeles district representated by Democratic Rep. Maxine Waters (though they also come in just below that cutoff in Democratic Rep. Karen Bass' nearby district).

For a variety of reasons, the groups favorable to Sanders could constitute a somewhat smaller share of the actual, rather than eligible, voters in these districts. College-educated whites consistently turn out to vote at higher rates than whites without degrees, according to census data, and the same is true for African Americans compared with Hispanics. And because whites without degrees have migrated toward the GOP so steadily in recent years -- especially during the Donald Trump era -- fewer of them may be inclined to participate in a Democratic primary. The reverse is true for college-educated whites, whose long-term movement toward the Democrats has accelerated in the Trump years. (Compared with 2016, whites with college degrees have increased their share of the vote in each of the first four 2020 contests except New Hampshire.)

Yet even with those caveats, the substantial contrast in the distribution of these groups underscores short-term and long-term challenges for the candidates hoping to dislodge Sanders from his leading position, a group now clearly led by Biden.

The short-term challenge is to minimize the delegate advantage Sanders is likely to amass on Super Tuesday, in particular across California and Texas. Both states are configured in a manner that almost perfectly matches Sanders' coalition. In California, Latinos and non-college whites combined represent a majority of the eligible voters in two-thirds of the districts and at least one-third of the eligible voters in fully 94% of them, according to the USC calculations. In Texas, those two groups represent a majority of the eligible voters in nearly four-fifths of the districts and make up at least one-third in all of them.

One asset for Biden and the others chasing Sanders may be a regional variation in the preferences of Latino voters. In California, Pastor notes, Latinos tilt to the left, in part because of the heavy influence of powerful labor unions across the state -- a dynamic similar to Nevada. But in Texas, a state without a strong labor presence, more Latinos have gravitated toward the center or even the right, Pastor notes. And that should help Biden compete among them in Texas more effectively than polls signal he's likely to do in California.

"Latinos in Texas have been tied to a more traditional politics, connected to elected officials, whereas in California the Labor-Latino alliance has been the driving force," Pastor said. "There's a lot of geographic nuance."

The same variation, he notes, in turn could help Sanders contain his losses among African American voters. Biden's strength could peak among black voters in the Southeast steeped in the cradle of the civil rights movement, but it may not be quite as imposing elsewhere, Pastor predicts. In fact, in 2016 exit polls found that Sanders ran somewhat more competitively among African American voters in several of the Midwestern battlegrounds -- including Michigan and Wisconsin -- than he did in the South.

Beyond Super Tuesday

If survival is the Super Tuesday goal for Sanders' rivals, their long-term challenge is to blunt his strengths and consolidate his vulnerabilities among white voters. For Democrats, no question about the race may be more uncertain than how college-educated white voters will break if the race functionally reduces to a two-person contest between Sanders and Biden after today. Neither one has been especially well positioned with those voters, though Biden ran much better among them in South Carolina than in the first three states. Through the first contests, a substantial portion of those voters have gravitated toward Buttigieg, who quit the race on Sunday; Klobuchar, who followed him off the field on Monday; and Sen. Elizabeth Warren of Massachusetts, who has not finished higher than third in the first four contests.

Even so, in such a two-person race, the key question may be whether Biden, who styles himself as "middle-class Joe," can blunt, or overcome entirely, Sanders' advantage among working-class whites. Biden's camp is optimistic he can, and some unaligned Democratic operatives agree.

"Biden's roots and history and commitment with those voters, with the blue-collar voters, will help him here. As long as he's not wounded coming out of Super Tuesday, then he could potentially get his bounce back and in some ways rehabilitate his campaign," says Jeff Rusnak, a Democratic consultant based in Ohio, a state with a large number of blue-collar white voters. "There is an opportunity for that here. Whether he has the money or not to do that, that's the challenge. Right now, there is no media, no ground game being waged by them. The Bernie folks are everywhere; they do have a ground game."

Still, Sanders' position has been especially strong, and Biden's catastrophically weak, among younger blue-collar whites. In each of the first four states, Sanders carried 50% to 61% of non-college whites younger than 45, according to an analysis of the exit polls by the CNN polling unit. Among those younger blue-collar whites, Biden carried just 5% in Nevada and New Hampshire, 7% in South Carolina and, incredibly, only 1% in Iowa. The former vice president has run more competitively with older blue-collar whites, but he's carried them only in South Carolina.

The next stages of the calendar will minimize Sanders' advantages among Latinos: There are fewer states where they are a major component of the electorate, and in Florida, the largest of them, he could face a backlash among Cuban Americans for his positive comments about the late dictator Fidel Castro. But if Biden can't improve his performance among working-class whites, even solid African American support might not be enough for him to overtake Sanders in the big Midwestern battlegrounds impending on the March calendar, including Missouri, Michigan, Illinois and Ohio.

After today, states with 123 total congressional districts will vote through the remainder of March. Whites without college degrees compose half or more of eligible voters in 60 of them and at least one-third in 94, according to the USC calculations.

In a one-on-one race with Sanders, Biden likely wouldn't need to win most of those voters, given his strength with African Americans and the potential resistance to the senator among well-educated whites. But Biden can't let Sanders sustain the lopsided advantages the senator has posted among those working-class whites in the first four states. Tonight may be the first indication of whether the former vice president can begin closing that gap.