This post is part of Polyarchy , an independent blog produced by the political reform program at New America , a Washington think tank devoted to developing new ideas and new voices.

After the results of the Indiana and North Carolina primaries on May 6, 2008, NBC's Tim Russert announced that Hillary Clinton had effectively lost the Democratic nomination to Barack Obama: "We now know who the Democratic nominee is gonna be, and no one's gonna dispute it."

The same is true this year; we have known that Clinton will be the nominee for at least a month (when she took a delegate lead of more than 700 after wins in Florida and Ohio). By the Associated Press's count, Clinton now has a 682-delegate lead over Bernie Sanders and needs only 625 more delegates (out of 1,775 still available) to officially clinch the nomination.

This margin is not well-known, because both campaigns (and the media) have avoided telling the public that the race is over as a result of the choices made by superdelegates, unpledged party officials who automatically receive votes at the national convention. Clinton is also well ahead in pledged delegates won in primaries, so her campaign would like to avoid the impression that she is relying on superdelegates to win.

The Sanders campaign is complaining about the role of superdelegates in the nomination process, but is implying that there is tremendous uncertainty about their eventual support, promising an "open convention." This has led to some media discussion that we are headed to a contested Democratic convention.

The impression is based on erroneous analogies to the 2008 Democratic race. That year, Obama successfully convinced most superdelegates that they should support him as the winner of the most pledged delegates. Sanders's supporters imply that the same will happen this time. But they leave out a fundamental difference: Clinton is currently winning superdelegate endorsements 469 to 31, with just over 200 yet to endorse. In other words, Sanders has already lost the superdelegate race by a large margin.

The role of superdelegates in 2008

In 2008, Clinton's January superdelegate lead of fewer than 100 slowly evaporated over the campaign as a result of new endorsements for Obama. The chart below provides weekly updates on 2008 superdelegate endorsements (from DemConWatch), showing that Obama took the superdelegate lead (to match his pledged delegate lead) directly following Russert's declaration of the race's end.

This year, by contrast, has seen little movement toward Sanders and no sign that a majority of superdelegates will switch allegiances based on the conclusion of the race. The Sanders campaign is projecting optimism to raise hopes among supporters, but there are not enough uncommitted superdelegates to make up his deficit.

All major news networks declared Obama the presumptive nominee on the final day of primaries, June 3, 2008, after he received 60 new superdelegate endorsements alongside new pledged delegates. Russert saw the inevitable win a month earlier, but the networks waited until Obama had accumulated a majority of delegates to officially call the race.

The Sanders campaign has argued that Clinton needs to clinch the nomination with pledged delegates alone this year or the convention will be contested, but Obama never met that standard: By pledged delegates alone, he was more than 350 delegates short of a majority. He relied on superdelegates to put him over the top.

The same will be true of Clinton this year; by all projections, she will be declared the winner of the nomination on June 7, when she eclipses 1,938 total delegates (including superdelegates). Even extraordinary Sanders gains would only get him to a majority of pledged delegates, not enough to overtake Clinton in total delegates.

Why Sanders is still fighting a losing battle

Despite Clinton's insurmountable lead, Sanders has little reason to leave the race. He is raising $40 million per month and helping lead a movement of young people to change the Democratic Party. Providing his supporters with hope that superdelegates will switch their endorsements is the only strategy remaining, but the 2008 campaign is not a model. A small number of Clinton supporters did change their endorsements at the end of the 2008 race, but only to signal that she should end a campaign that was already lost. The vast majority of Obama superdelegates came from among the previously uncommitted.

Clinton did not officially end her 2008 campaign until June 7. Like Sanders, she did not give up before exhausting all options. She campaigned through the entire primary calendar. She contested the reduced voting power of the Florida and Michigan delegations at the Rules and Bylaws Committee. She lobbied superdelegates, asking them to consider that she had won more total votes and more states and might be a stronger general election candidate. There is no reason to expect an anti-establishment candidate like Sanders to have more success convincing delegates to switch their votes this time.

Sanders will have arguments to persuade superdelegates this year as well, but to imagine that he will convince hundreds of them to renounce their prior support of Clinton is fanciful. Superdelegates have traditionally favored the clear pledged delegate winner, but prior races do not provide a precedent for a large shift in support among the already committed.

Even if, against all odds, Sanders ekes out a win among pledged delegates, he will remain behind Clinton in votes cast. An improbable come-from-behind lead among pledged delegates would certainly offer a new argument for Sanders, but it is not a recipe for Democratic elites to suddenly desert Clinton. Superdelegates are likely to want the race behind them, not convention chaos to match the Republicans.

Sanders may still take the race to the convention in some form. He has less to gain from appeasing the party than Clinton did in 2008, when she remained a likely future candidate. As a longtime independent, Sanders has far fewer institutional ties to the party. He could instead follow the 1992 precedent of Jerry Brown, who refused to end his campaign despite having no chance to win. Brown even seconded his own nomination at the convention to give himself an opportunity to speak.

Another precedent comes from the 1980 Democratic convention, where the Ted Kennedy campaign asked delegates to change the rules to unbind their votes from the primary results in order to support him. The delegates were in no mood to abandon Jimmy Carter.

Sanders may follow these examples and provoke some theatrical drama in Philadelphia this year, though it will not match the real potential uncertainty at the Republican National Convention in Cleveland. The lesson from 2008 is that the path to becoming the presumptive nominee includes accumulating support from all delegates (including those who are officially uncommitted until the convention vote). News organizations have considered superdelegate support in prior cycles when declaring the presumptive nominee and will again this year.

If Bernie Sanders had obtained more support among party leaders and elected officials months ago and slowly built their support throughout the campaign, he might be able to rely on the chance of a last-minute surge in superdelegate support to gather remaining uncommitted votes. Instead, superdelegates are supporting Clinton by a 10-to-1 margin, with most already committed, and there is little reason to expect significant change.