The Democratic primary season comes to a climax on Tuesday, when six states will vote: California, Montana, New Jersey, New Mexico, North Dakota, and South Dakota. The biggest prize is California, where the race appears to be tightening. On Thursday, the widely respected Field Poll showed Hillary Clinton leading Bernie Sanders among likely voters by just two points, forty-five per cent to forty-three.

Having lost four of the last five primaries on the U.S. mainland, Clinton would dearly love to defeat Sanders in California, his chosen battlefield, and give her campaign fresh momentum going into next month’s convention. Sanders, for his part, is still hoping that a come-from-behind victory in California will help him persuade large numbers of superdelegates to switch sides, enabling him to capture the nomination in Philadelphia. “If the voter turnout is high, we will win California, and we stand a chance to win it with a big margin,” Sanders said at a press conference on Saturday. He went onto say, “The Democratic National Convention will be a contested convention.”

That last statement represented a rhetorical escalation. Even if Sanders does carry California, Clinton is virtually certain to retain her lead in elected delegates, which currently stands at two hundred and sixty-eight, according to atally by the Times. Because California’s five hundred and forty-six delegates will be divided in proportion to votes, Clinton is guaranteed to win a good number of them. And she is favored to come out ahead of Sanders in New Jersey and New Mexico, which between them have a hundred and eighty-five delegates.

If Clinton ends the primary season with a substantial lead in elected delegates, she will be hailed as the presumptive nominee. But Sanders seems determined to take his argument to the superdelegates: seven hundred and nineteen current and former Democratic Party officials. “Hillary Clinton will not have the requisite number of pledged delegates to win the Democratic nomination at the end of the nominating process on June 14th. Won’t happen. She will be dependent on superdelegates,” Sanders said. Right now, five hundred and forty-four of the superdelegates are committed to Clinton; just forty-six are committed to him.

The Vermont senator’s argument to the superdelegates will be that he has a better chance of defeating Donald Trump. To strengthen this argument, he badly needs to carry California, a huge and diverse state where the demographics appear to favor Clinton. In the 2008 Democratic primary, about thirty per cent of voters were Latinos, a group that has tilted heavily toward Clinton in earlier primaries. Clinton also has some significant endorsements in the state, including one from Governor Jerry Brown, a popular figure who ran in the 1992 Democratic primary as a Sanders-style insurgent against Bill Clinton.

But Sanders also has a number of advantages. All along, he has done much better in open primaries, where independents as well as registered Democrats can vote. In California, independents, who are officially referred to as “non-partisans,” are eligible to vote as long as they registered by May 23rd. A second factor in Sanders’s favor is that, in recent months, the state has seen a surge in voter registrations, particularly among young voters, who skew heavily toward him. According to figures from the office of California’s Secretary of State, between mid-March and mid-May the number of registered Democrats rose by more than two hundred and twenty thousand, or about three per cent.

In Los Angeles County alone, almost two hundred thousand voters have registered since the start of the year, and more than sixty per cent of them were under the age of twenty. One independent expert, Paul Mitchell, of Political Data Inc., calculated that, since 2012, as many as two million new voters have joined the electoral register statewide, many of them under the age of thirty.

These figures augur well for Sanders, as does some of the recent polling data. The Field Poll showed him running ahead of Clinton in the northern half of the state, including the Bay Area. Clinton was doing best in Los Angeles County and the Central Valley, both of which have large minority populations. However, the poll also showed that, among Latino voters, Clinton was leading Sanders by just four points, forty-six per cent to forty-two. As was the case in many other states, there appears to be a large gender gap in California. Among men, Sanders was leading in the Field Poll by eleven points; among women, Clinton was ahead by nine.

The most recent poll from the Los Angeles Times, which was also published on Thursday, showed the contest virtually tied among registered voters, but among “likely voters” Clinton retained a ten-point lead. These figures raised the question of who is genuinely likely to turn out. Many of Clinton’s supporters are older people and loyal Democrats, who tend to vote pretty reliably. Sanders is counting on young people, independents, and other groups that have a lower propensity to actually appear at the polling stations. Getting enough of these voters to show up on Tuesday will be a big task. How big? “This may be the biggest voter mobilization challenge California has seen in many, many years,” Dan Schnur, the director of the Los Angeles Times poll and the head of U.S.C.’s Jesse M. Unruh Institute of Politics, said.

Sanders, in his press conference on Saturday, acknowledged that he needed a large turnout, but he sounded confident. Clinton, however, remains the forecasters’ favorite. Although her lead has narrowed in the polls, no survey has shown Sanders ahead. On Sunday, FiveThirtyEight’s “polls-plus” forecast, which combines polling numbers with data on endorsements, put the probability of a Clinton victory in California at ninety-two per cent. Predictwise, a site that combines polling data with information from prediction markets, estimated that she has a seventy-per-cent chance of winning.

The polls have been wrong before, of course, and, rather than making a prediction, I’d rather wait for the outcome. Even though it’s unlikely to affect who gets the nomination, it could have a major impact on where the Democratic Party goes from here—toward unity or discord.