Story highlights Sanders penned the book endorsement for "Buyer's Remorse: How Obama let Progressives Down" by Bill Press

"Bill Press makes the case why, long after taking the oath of office, the next president of the United States must keep rallying the people who elected him or her on behalf of progressive causes," Sanders said

(CNN) Bernie Sanders' presidential campaign on Saturday stood by a book endorsement the Vermont senator wrote that suggested President Barack Obama had let progressives down, claiming that what the senator wrote is "absolutely true."

Sanders penned the book endorsement for "Buyer's Remorse: How Obama let Progressives Down" by Bill Press. "Bill Press makes the case ... Read this book," Sanders writes in a blurb featured atop the book's front cover.

"Bill Press makes the case why, long after taking the oath of office, the next president of the United States must keep rallying the people who elected him or her on behalf of progressive causes. That is the only way real change will happen," read Sanders' full quote. "Read this book."

On Saturday, Michael Briggs, Sanders' spokesman, stood by the comment.

"What Senator Sanders said in that book blurb is absolutely true," Briggs said. "The next president must do everything possible to reinvigorate American democracy and get working people to stand up for their interests. This country, under the outstanding leadership of President Obama and Vice President Biden, has come a very long way since President Bush left office."

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