Sen. Bernie Sanders is taking the high road after Hillary Clinton complained about the damage to her presidential bid inflicted by Sanders's own campaign in her forthcoming book. It's just that the road is covered in shade.

Appearing on CBS's “Late Show” with Stephen Colbert on Thursday, the senator from Vermont didn't say that the former Democratic nominee has only herself to blame for her loss to Donald Trump — or anything so directly confrontational. In fact, Sanders said he understands why Clinton would resent him for a tough (and long) primary fight.

Rather than concede some merit to Clinton's gripe, however, Sanders suggested that his former rival is simply venting her emotions.

“Look, you know, Secretary Clinton ran against the most unpopular candidate in the history of this country, and she lost,” Sanders told Colbert, when asked about Clinton's book. “And she was upset by that. I understand that.”

Notice how Sanders suggested that President Trump was a weak election opponent, a not-so-subtle jab that implies Clinton choked in November.

Hillary Clinton's new book, 'What Happened,' published Sept. 12 and aims to "pull back the curtain" on her losing presidential bid. (Monica Akhtar/The Washington Post)

Sanders is promoting his own book right now: “The Bernie Sanders Guide to Political Revolution.” But Colbert mostly wanted to talk about Clinton's reflection on the 2016 campaign.

COLBERT: Somebody else has a book right now. Hillary Clinton does. And that book is called “What Happened.” And, uh, she remembers you from the campaign in the book. I don't know if you're aware of this, but I'd like your reaction to this: Hillary Clinton says that your attacks during the campaign caused lasting damage, making it harder to unify progressives. What is your response to that accusation — that you damaged America by damaging Hillary Clinton?

SANDERS: Actually, the case is that the progressive movement today and grass-roots activism is stronger than it has been in many, many years. As a result of our campaign, millions of young people began to vote for the first time, became engaged in the political process. We're seeing young people all over this country, working-class people, running for office, from school board to Congress. So, I think there is a level of understanding now among people — and what [my] book is about — that we have got to stand together against Trump's efforts to divide us up, take on the billionaire class and make that political revolution, so that we have a government that works for all of us, not just the 1 percent.

Sanders's response was a bit of a sidestep. He certainly deserves credit for engaging young voters, but he arguably accomplished that goal long before he finally threw his support behind Clinton in July 2016, without actually suspending his own campaign. He didn't really address the charge that he stayed in the race too long and hindered Clinton's ability to rally the entire Democratic base.

Should Clinton care to make this argument (again), she will have an opportunity when she takes her turn on Colbert's set later this month.

From jokes about the election outcome and the inaugural crowd size to warnings about the Trump administration's growing Russia scandal, Hillary Clinton has turned her ire on President Trump. (Jenny Starrs/The Washington Post)