Democratic presidential candidate Bernie Sanders responded to a question about Hillary Clinton's e-mails. (CNN)

Much political chatter this week focused on a pivotal moment at Tuesday night’s CNN Democratic debate in Las Vegas: “I think the secretary is right, and that is that the American people are sick and tired of hearing about your damn e-mails,” said Sen. Bernie Sanders to former secretary of state Hillary Clinton. Sanders was called upon to address the Democratic front-runner’s ongoing e-mail controversy after Clinton issued her standard defense.

The Vermont senator’s defense brought an uproarious reaction from the crowd at the Wynn Las Vegas. Though hopefuls Lincoln Chafee and Martin O’Malley both chimed in on the e-mail stuff, Sanders had pretty well snuffed out the issue. “Thank you, Bernie. Thank you,” said Clinton after Sanders had ripped the e-mail stuff as a campaign-trail issue.

In a chat with former New York Times television reporter Bill Carter on the SiriusXM show “The Bill Carter Interview,” Cooper put this moment in his basket of regrets over his handling of the debate. “I wish I had brought in one other candidate before I went to Sanders on the email thing because I knew Sanders would try to shut it down,” said the debate host. Perhaps that would have been a better way to go, though there was no guarantee. After all, Chafee commented that the e-mails drive at a credibility crisis in American politics. When Cooper asked Clinton whether she wanted to respond, she said, “No,” to the delight of her supporters.

The assembled challengers weren’t prepared or disposed to mount a serious challenge to Clinton’s e-mail problem. That would have had to come directly from Cooper in a series of pointed questions. Posing them would have hijacked the debate, driving it into a homebrew rabbit hole; better to leave the prolonged e-mail cross-examinations to Cooper’s peers who sit for extended interviews with the candidate. Several such clashes have already taken place, and there are more to come, including Jake Tapper’s CNN interview with Clinton this afternoon.

In the Carter interview, Cooper asked himself: “Was I too tough on Lincoln Chafee?” That was an apparent reference to Cooper’s merciless pursuit of Chafee over his 1999 vote for legislation that enabled banks to grow bigger, even though Chafee has criticized Clinton for coziness with Wall Street. Transcript:

COOPER: Governor Chafee, you have attacked Secretary Clinton for being too close to Wall Street banks. In 1999 you voted for the very bill that made banks bigger.

CHAFEE: The Glass-Steagall was my very first vote, I’d just arrived, my dad had died in office, I was appointed to the office, it was my very first vote.

COOPER: Are you saying you didn’t know what you were voting for?

CHAFEE: I’d just arrived at the Senate. I think we’d get some takeovers, and that was one. It was my very first vote, and it was 92-5. It was the…

COOPER: Well, with all due respect, Governor…

CHAFEE: But let me just say…

COOPER: … what does that say about you that you’re casting a vote for something you weren’t really sure about?

CHAFEE: I think you’re being a little rough. I’d just arrived at the United States Senate. I’d been mayor of my city. My dad had died. I’d been appointed by the governor. It was the first vote and it was 90-5, because it was a conference report.

In answering his own question, Cooper said, “I never want to be rude to anybody. Someone once said to me a saying their grandfather had told them, which is, I’m mangling the phrase: ‘It’s a lot harder to be kind than it is to be clever. Or it’s very easy to be clever, being kind is hard.’ And my mom has a saying from a guy named MacLaren who said, ‘Be kind because everyone you meet is fighting a great battle.’ And I take that very much to heart. I think that’s very true, and I think it’s very easy in this day and age not to be kind and to be clever….And being clever is usually at somebody’s expense. And being kind is actually hard. And you know what, everybody is fighting a great battle in one way or another whether you see their scars or not.”

Not sure what that all means, other than that Cooper is a thoughtful guy.