Lincoln Chafee suffered perhaps the roughest moment of the Democratic debate on Tuesday night when he implied he did not know what he was doing when he voted in the Senate to allow greater consolidation of the U.S. banking system.

The former Rhode Island governor, who has for months been stuck near zero percent in national polls, had no answer when CNN moderator Anderson Cooper asked how Chafee could attack Hillary ClintonHillary Diane Rodham ClintonHarris lists out 'racist' actions by Trump in '60 minutes' interview: 'It all speaks for itself' Trump has list of top intelligence officials he'll fire if he wins reelection: report Clinton says most Republicans want to see Trump gone but can't say it publicly: report MORE for being too close to Wall Street banks when in 1999 Chafee voted in the Senate "for the very bill that made banks bigger," a repeal of the Glass-Steagall Act that had kept traditional and investment banking separate.

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"Glass-Steagall was my very first vote. I'd just arrived, my dad had died in office," said Chafee, referring to his vote for the Gramm-Leach-Bliley Act.

"Are you saying you didn't know what you were voting for?" Cooper asked.

"I'd just arrived in the Senate. ... It was my very first vote," Chafee said.

"With all due respect, what does that say about you that you were casting a vote for something you weren't really sure about?" Cooper said.

"I think you're being a little rough," Chafee replied. "I'd just arrived at the United States Senate."

Chafee, who has failed to generate any momentum so far in his primary campaign, tried more than any other candidate on the debate stage to attack Clinton over ethical issues. 

In his opening and closing remarks, Chafee took unsubtle swipes at Clinton, boasting that he was proud of having "no scandals" during his 30 years of public service.

But the partisan audience at the Wynn hotel-casino in Las Vegas was clearly on Clinton's side.

Late in the debate, when Cooper raised the issue of Clinton's controversial use of a private email server during her term as secretary of State, Chafee took another opportunity to challenge her ethics.

"I think we need someone that has the best in ethical standards as our next president," Chafee said. 

Cooper asked Clinton whether she would like to respond to Chafee's charge.

"No," she replied to cheering, whistling and laughter from the crowd.