Bernie Sanders is aware that Hillary Clinton’s new book What Happened reveals her to be, uh, less than thrilled with his campaign for president, suggesting he hurt hers with undue attacks and pie in the sky promises. But while promoting his own book (Bernie Sanders Guide to Political Revolution) last night, Sanders insisted to Stephen Colbert that he’d rather not retroactively dissect the 2016 election ever again.

“Secretary Clinton ran against the most unpopular candidate in the history of this country, and she lost. She was upset about that, I understand,” the senator shrugged after Colbert kept pressing for a response. “But our job now is really not to go backwards. It is to go forwards. It is to create the nation we know we can become. We have enormous problems facing us, and I think it’s a little bit silly to keep talking about 2016.”

But Colbert knew he had an opportunity, having Sanders on his show so soon after Clinton’s book excerpt came out, so he wasn’t so easily deterred from going backward for the interview. And when Colbert asked Sanders if it was fair for Clinton to deride his campaign promises as too unrealistic, Sanders got animated as he issued an unequivocal no. He then tried to shoot down the accusation that he sold a “pipe dream” by pointing to growing support for single-payer health care and raising the minimum wage as corollary victories from his campaign.

“The real point is, we broke through a box which said you can’t talk about this, you can’t talk about income equality, health care for all, taking on the billionaire class,” Sanders said. “We did it. We got 13 million votes. I think we helped transform politics in America.”

As far as Sanders is concerned, that is pretty much that. There’s no question that people will continue to dissect the nuances and failures of the 2016 campaigns whether Sanders likes it or not, but his final word on the subject — at least for now, he’s still got a book to sell, after all — is that he “would like [Clinton] to join us in the fight.”

“We need her help to go forward,” Sanders concluded. “Let’s not keep arguing about 2016.”