A document leaked by a hacker who took responsibility for the Democratic National Committee data breach appears to show the DNC coordinating with Hillary Clinton from the start of the presidential campaign — just as Bernie Sanders has claimed.

A document to the DNC dated May 26, 2015 — a month after Sanders kicked off his presidential bid — declared that “our goals & strategy” are to “provide a contrast between the GOP field and HRC.”

HRC stands for Hillary Rodham Clinton.

The document, posted online by the hacker “Guccifer 2.0,” outlines ways to hit back at the GOP presidential field, such as “use specific hits to muddy the waters around ethics, transparency and campaign finance attacks on HRC.”

The author of the document is not listed. The DNC stayed officially neutral during the prolonged primary between Clinton and Sanders.

But some Sanders backers say the document shows what they’ve felt all along: The system was rigged in favor of Clinton.

“With proof that #Bernie never even had a chance, I shall double down and vote #BernieOrBust in Nov. @TheDemocrats,” tweeted a Sanders supporter from Chicago.

Sanders has declined to drop out of the Democratic primary race. Among his demands to Clinton and the Democratic National Committee: Oust DNC leader Debbie Wasserman Schultz and get rid of superdelegates.

“There are lots of valid reasons to question Schultz’s leadership, including how the DNC conducted itself during this last primary election season,” Sanders backer Ben Jealous, former head of the NAACP, told The Post. “However, what is just as concerning is how the party has performed in general under her leadership.”

The DNC confirmed the computer break-in earlier this week and blamed Russian government hackers.

A senior DNC official stands by the assessment despite Gussifer’s claim it was a “lone hacker.”

“We believe that today’s release and the claims around it may be a part of a disinformation campaign by the Russians,” the official said, declining to address the alleged collusion. “We’ve deployed the recommended technology so that today our systems are secure thanks to a swift response to that attack and we will continue to monitor our systems closely.”