Fox News' contributor Dan Henninger said Sen. Bernie Sanders’ weaknesses were on full display during the 2020 Democratic presidential debate last night in Las Vegas.

“I think some real Sanders' vulnerabilities were opened up in that debate," Henninger told “America's Newsroom.” “Mike Bloomberg cited the fact that capitalism isn’t going away in this country made Bernie, frankly, say I am a Democratic-Socialist. Flat-out."

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Bloomberg said that Sanders’ failure to address the $25 trillion hole in his health care plan, pointed out by former South Bend, Ind., Mayor Pete Buttigieg, was another “vulnerability.”

Furthermore, Henninger said Sanders’ vow to “ban fracking,” followed up by his assertion that workers in the fracking industry will just have to “get over it” hurts his candidacy.

“How is that going to play with those people that have jobs related to the energy industry in the Midwest?” Henninger asked.

Sanders also defended his label of being a Democratic socialist on Wednesday night at the Democratic debate in Nevada. The progressive senator has been enjoying a surge in the polls in recent weeks, including an NBC News/Wall Street Journal poll released Tuesday that showed him with a national double-digit lead -- 27 percent of support, which is well ahead of former Vice President Joe Biden and former New York City Mayor Michael Bloomberg, who earned just 15 and 14 percent, respectively.

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During the debate, NBC News moderator Lester Holt asked Sanders about the poll result.

"Our latest NBC News/Wall Street Journal poll released yesterday -- two-thirds of all voters said they were uncomfortable with a socialist candidate for president. What do you say to those voters, sir?" Holt asked.

"What was the result of that poll?" Sanders countered. "Who was winning?"

Some in the audience applauded Sanders for challenging the question.

"The question is to you," Holt continued.

"Well, the question was, 'Was I winning' -- and I think by a fairly comfortable margin -- might mention that," Sanders added.

Fox News' Joseph A. Wulfsohn contributed to this report.