Story highlights Clinton characterized Sanders as an unrealistic over-promiser in her book

She said that his attacks against her during the primary caused "lasting damage"

Washington (CNN) Vermont Independent Sen. Bernie Sanders on Wednesday shrugged off criticism made by his former presidential primary challenger Hillary Clinton in her new book about the 2016 election, saying that he's instead focused on new issues.

"My response is that right now it's appropriate to look forward and not backward," he said in a statement. "I'm working overtime now to see we overturn (President Donald) Trump's decision on (the Deferred Action for Childhood Arrivals program), pass a $15-an-hour minimum wage and next week I'll be offering a Medicare-for-all single-payer system."

"Our job is to go forward," he added.

His comments refer to passages in Clinton's new book, "What Happened," which lobbed some heavy criticism at her former Democratic challenger. CNN obtained a copy of the book earlier this week.

In it, Clinton characterized Sanders as an unrealistic over-promiser.

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