As Bernie Sanders reaffirms his pledge to contest the Democratic presidential nomination all the way through July’s party convention, one of his fundamental obstacles remains his consistent weakness among voters who identify as actual Democrats.

Results from the exit polls conducted in 27 states through the nominating contest so far show that Hillary Clinton has established a huge lead over Sanders among voters who self-identify as Democrats. Sanders, though trailing in the popular vote and delegate count, has remained competitive only because he has built a virtually identical lead among primary voters who self-identify as independents.

This pattern has persisted across all regions of the country and crystallizes the offsetting strengths and weaknesses that have defined the two combatants through their unexpectedly extended contest.

Across the 27 exit polls, voters who identify as Democrats have cast exactly three-fourths of the ballots in the primaries, according to new figures provided by CNN Polling Director Jennifer Agiesta. Those Democratic voters have preferred Clinton over Sanders by a cumulative margin of 64 percent to 35 percent.

Independents and Republicans have comprised 22 percent of the total primary electorate. Among those voters from outside of the Democratic Party, the results are almost exactly reversed: they have preferred Sanders by an equally emphatic 64 percent to 34 percent.

Because Democrats so outnumber the non-Democrats participating in the process, Clinton has amassed a lead over Sanders of about three million in the combined vote in all the primaries and caucuses so far. She has also beaten him in 14 of the 18 largest states that have voted.

Although Clinton is virtually certain to emerge from tomorrow’s voting with enough pledged and unpledged superdelegates to reach the 2,383 required for the nomination, Sanders has not signaled that he’s ready to concede. If he can win the closely-fought the California primary his campaign says it intends to highlight his strength among independents in an uphill effort to convince some of those unpledged superdelegates to abandon their support for Clinton.

“That is the reason why he is a stronger candidate in the general election,” said Tad Devine, Sanders’s senior strategist. “The Democratic Party is going to make some decisions about this election and also about its future: do we want to have a party which resists bringing people in who are inclined not to identify as Democrats, particularly among these young people where the disinclination [to join] a party is most intense?”

But Mark Mellman, a long-time Democratic pollster unaffiliated in the race, says that any argument from Sanders isn’t likely to dislodge superdelegates once Clinton’s combined pledged and unpledged delegate support passes the 2,383 milepost, as seems certain tomorrow. “There’s really no argument he can make [to superdelegates],” says Mellman. “She’s got the most total votes, she’s got the most votes from Democrats; she’s got the most pledged delegates and she’s got the most unpledged delegates.”

The epic 2008 race between Clinton and President Obama also generated a partisan divide in the primary vote—but not one nearly this stark. In that race, Clinton narrowly beat Obama among self-identified Democrats by a 51 percent to 45 percent margin, while he topped her among independents by 52 percent to 40 percent, according to a cumulative ABC analysis of the 39 exit polls conducted that year.

The new CNN data consolidating the results from all 27 exit and entrance polls conducted in the Democratic primary this year show a much wider partisan gap between Clinton and Sanders. While Clinton last time ran 11 percentage points better among Democrats than independents, this time the difference in her support is 30 points. Obama in 2008 ran seven percentage points better among independents than Democrats; for Sanders, the gap is 29 points, four times as wide.

Of the 27 exit-polled states, Sanders has carried most Democrats only in his home state of Vermont and neighboring New Hampshire. The two also tied among them in Wisconsin. But Clinton has carried self-identified Democrats in all other 24 states with exit polls.

It’s possible—even likely—that Sanders also won Democrats in some of the caucus states that he carried, where exit polls were not done. But exit polls were conducted in all of the larger states that have voted so far (except for Arizona and Washington) and in those states self-identified Democrats have often preferred Clinton by crushing margins.

In 21 of the 27 exit-polled states, Clinton has carried at least 55 percent of self-identified Democrats. In the ten largest states that have voted, Clinton has reached at least 62 percent of the vote among self-identified Democrats in all except Illinois (where she won 55 percent) and Michigan (58 percent). In the two largest remaining states that will vote, Clinton appears on track for a comfortable win among Democrats (and overall) in New Jersey. While polls in California show a close race overall, most show her leading among self-identified Democrats, some by big margins.

Clinton’s advantage over Sanders represents a much more one-sided pattern than in 2008, when she carried self-identified Democrats in 23 states and Obama in 16, according to the exit polls.

One reason for Clinton’s lead over Sanders among Democrats is her big lead among minority voters. Across all 27 exit polls, Clinton has carried 78 percent of African Americans and 62 percent of Latinos, according to a separate cumulative exit-poll analysis conducted by the ABC pollster Gary Langer.

But, according to Agiesta’s figures, Clinton has also beaten Sanders soundly among white Democrats, by 56 percent to 43 percent. Sanders has carried 68 percent of white independents, compared to just 29 percent for Clinton. Overall white voters have split about evenly between the two, with Clinton drawing 48 percent and Sanders 50 percent.

Paul Begala, a long-time Democratic strategist advising the pro-Clinton Priorities USA Action political action committee, attributes her advantage among Democrats to the convergence of several factors. “A lot of it is she’s spent a life time in the party and he’s spent a lifetime outside the party,” Begala said. “And Democrats are more moderate than socialists are. Plus he’s never been able to appeal to large numbers of people of color.”

Sanders has remained competitive largely through his strength among voters who do not identify as Democrats, particularly independents. He’s carried independents in all of the 27 exit-polled states except Mississippi, Alabama, and Georgia. Sanders has reached 55 percent or more of the vote among independents in 20 states, and has exceeded 70 percent among them in several places, including Michigan and Wisconsin. (In 2008, Obama won independents in 29 states, Clinton in 8 and in two others they tied.)

Simon Rosenberg, founder of the Democratic advocacy group NDN, says Sanders’s strong performance among independents explodes the assumption that most of those voters are moderates who place themselves somewhere between Democratic liberalism and Republican conservatism. Instead, he argues, Sanders’s strong showing indicates that what most unites independents at this point is the belief that both parties, and the political system more broadly, has failed average Americans.

“To me the most significant thing that’s being seen about Bernie is his condemnation of the political system … as corrupt and not working for every day people,” says Rosenberg. “It’s one of the reasons he is doing so well, despite being a ‘leftist,’ with independent voters.”

On the other hand, Rosenberg says, the inability to attract more Democrats “makes it hard” for Sanders to claim he deserves the nomination over Clinton. “His surge came too late for him to ever mount a challenge among traditional Democrats against somebody who [they] like and admire.”

Assessing these results, Devine, Sanders’s strategist, says “all of these state contests where independents chose [Sanders] overwhelmingly are his best evidence” that he would be a stronger nominee than Clinton against Trump.

But Mellman maintains that argument is fundamentally flawed. “There is absolutely no relationship between winning independents who vote in a Democratic primary and winning independents more generally,” he says.

The exit polls measure self-identification, not legal voter registration, so some people who identify as independents in them might in fact be registered as Democrats (or vice versa). But the trend of contrasting strength for Clinton among Democrats and Sanders among independents tracks the actual results across the primary calendar. Heading into tomorrow’s final round of contests, Sanders has won nine primaries (the rest of his 20 victories came in caucuses). Of those nine primaries, all but Oregon allowed independents to participate. Sanders’s campaign itself has underscored its reliance on open contests, by putting all of its chips on California, an open primary, while essentially conceding to Clinton in New Jersey, the nation’s 11th-largest state, but a primary in which only Democrats can vote.

The decision to essentially abandon New Jersey to focus entirely on California contravenes Devine’s indication from several weeks ago that Sanders would need to win both to have any chance of convincing super delegates to defect from Clinton on the grounds that he would be a stronger general election nominee. Even now, Devine acknowledges that case will be weakened if Sanders can’t finish competitively there, whatever happens in California.

“If we win California, we come close in New Jersey, we win Montana, North and South Dakota and maybe New Mexico, I think that’s a pretty strong close for us,” Devine said. “If we can pull that [off] … there is going to be a lot of dust that settles the next day and we’ll just let it settle and that’s when we will decide what is the path forward, what options we have.”


Atlantic assistant editor Leah Askarinam contributed.