Sen. Bernie Sanders, I-Vt., appeared on The Late Show Thursday night.

In a late-night TV appearance Thursday, Sen. Bernie Sanders responded to criticism 2016 Democratic presidential nominee Hillary Clinton leveled at him in her forthcoming book.

In excerpts leaked earlier this week from Clinton’s book, she writes that Sanders’ primary attacks “caused lasting damage, making it harder to unify progressives in the general election and paving the way for Trump’s ‘Crooked Hillary’ campaign.”

Late night host Stephen Colbert, welcoming Sanders to his CBS show as the “raspberry seed in Washington’s wisdom tooth,” asked Sanders about the book excerpts.

“Look, Secretary Clinton ran against the most unpopular candidate in the history of this country and she lost, and she was upset about it and I understand that,” Sanders said.

Sanders encouraged a focus on the future, not on the past.

“We have enormous problems facing us and I think it’s a little bit silly to be keeping talking about 2016,” he said.

Sanders also responded to a section of Clinton’s book in which she accuses him of offering unrealistic promises, claiming widespread public support for his trademark initiatives like single-payer health care and raising the minimum wage.

Clinton will be making an appearance on the Late Show herself later this month. Colbert asked Sanders what he should ask her during her visit.

“We need her help to go forward. Let’s not keep arguing about 2016. Let’s get together, take on Trump’s desire to divide us up. Let’s go forward with a progressive agenda,” Sanders said.

“Ask her if she’ll do that,” he told Colbert, with a wave of one hand.

Twitter: @emhew. Elizabeth Hewitt is the Sunday editor for VTDigger. She grew up in central Vermont and holds a graduate degree in magazine journalism from New York University.