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.