(CNN) - Sen. Bernie Sanders of Vermont, an independent who caucuses with Democrats, had some biting criticism for President Barack Obama's debate performance, saying Thursday that the president took a "disastrous" approach in his match-up against Mitt Romney.
Asked to describe the president's demeanor on stage, Sanders said Obama did "poorly."
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"No question about it," Sanders said in his interview on CNN's "The Situation Room." "I think he was listless."
A CNN/ORC International Poll released shortly after the debate Wednesday night showed Romney overwhelmingly defeated the sitting president. Sixty-seven percent of viewers said the GOP nominee was the winner, with 25% saying Obama fared better.
Observers noted the president's tendency to avoid eye contact and his seeming lethargic, while Romney appeared to have more energy and looked at the president while speaking.
Sanders especially took issue with the president's strategy to reference positions the two candidates have in common. Throughout the night, Obama said he and Romney both agree that the corporate tax rate is too high, that America needs a boost in energy production, that some regulations are needed in the marketplace - and that he suspects the two have a "somewhat similar" position on Social Security.
The Vermont senator, however, said the president's decision to align himself with Romney - even if faintly - was a "disastrous approach."
"The truth of the matter is, Mitt Romney right now is the head of a right-wing extremist party called the Republican Party," he said. "And if the president cannot differentiate himself clearly from right-wing extremism, we have a lot of problems as a nation and he has a lot of problems as a candidate running for re-election."
The senator added that while Obama may have lost on style points, Romney lost on the merit of his policies.
"From a policy point of view and honesty point of view, Romney was a failure, as well," Sanders told CNN's Wolf Blitzer and Kate Bolduan.
Sanders was one of several left-leaning voices that offered disapproval of the president Thursday.
Responding to the criticism, Obama's campaign has maintained their candidate did well and proved far more honest than his opponent.
"Obviously, Mitt Romney had a good performance, but that's just what it was - it was a performance," Obama deputy campaign manager Stephanie Cutter said on CNN's "Erin Burnett OutFront."
"He wasn't leveling with the America people or being honest with them about his own policies."
Cutter continued, "Now that we know what we're dealing with in the Mitt Romney that showed up last night - I'm presuming he's going to show up in the next debate, too - We'll hold him accountable for the things that he's saying."