(CNN)Hillary Clinton casts Bernie Sanders as an unrealistic over-promiser in her new book, according to excerpts posted by a group of Clinton supporters.
She said that his attacks against her during the primary caused "lasting damage" and paved the way for "(Donald) Trump's 'Crooked Hillary' campaign."
Clinton, in a book that will be released September 12 entitled "What Happened," said Sanders "had to resort to innuendo and impugning my character" because the two Democrats "agreed on so much."
"Some of his supporters, the so-called Bernie Bros, took to harassing my supporters online. It got ugly and more than a little sexist," she wrote.
"When I finally challenged Bernie during a debate to name a single time I changed a position or a vote because of a financial contribution, he couldn't come up with anything," Clinton wrote. "Nonetheless, his attacks caused lasting damage, making it harder to unify progressives in the general election and paving the way for Trump's 'Crooked Hillary' campaign."
The excerpts were first posted by a pro-Clinton Twitter account and by a user on a Clinton "super volunteer" Facebook page.
"She says a lot in this book, and some of it is going to surprise people. People should buy it, read it, and consider what she constructively lays out. It's a great read," a Clinton aide said, asking not be named because they were not authorized to discuss the book.
The excerpts represent a small number of the roughly 500-page book in which Clinton reflects on her stunning loss to Donald Trump in 2016. The few pages on Sanders are also remarkably candid for a candidate who was more known for being careful than blunt, especially when it came to the Vermont senator.
A Clinton spokesman declined to comment on the published excerpts.