Vermont Sen. Bernie Sanders accused former Secretary of State Hillary Clinton of taking a "low blow" during Thursday's Democratic primary debate, after she equated his criticism of President Obama to the rhetoric of Republicans.

The exchanged came shortly after the two Democratic presidential hopefuls were asked by an audience member to "name two leaders, one American and one foreign, who would influence [their] foreign policy decisions?"

Sanders named former President Franklin D. Roosevelt and former British Prime Minister Winston Churchill. During her turn, Clinton answered the question, then quickly pivoted to attack her opponent.

"I certainly agree with FDR, for all the reasons Sen. Sanders said, and I agree about the role that he played both in war and in peace, on the economy and in defeating fascism around the world. I would choose Nelson Mandela for his generosity of heart, for his understanding of the need for reconciliation," Clinton said. "But I want to follow up on something having to do with leadership because today Sen. Sanders said President Obama failed the presidential leadership test."

She continued, "This is not the first time that he has critiqued President Obama. In the past, he's called him weak, he's called him a disappointment, he wrote a forward for a book that basically told Americans they should have buyer's remorse when it comes to President Obama's leadership and legacy – and I just couldn't disagree more with those kinds of comments."

"The kind of criticism that we've heard from Sen. Sanders about our president, I expect from Republicans," she charged. "I do not expect it from someone running for the Democratic nomination to succeed President Obama."

"Madam Secretary, that is a low blow," Sanders shot back.

"I have worked with President Obama for the last seven years," he said matter-of-factly. "When President Obama came into office, we were losing 800,000 jobs a month, we had a $1.4 trillion deficit and the world's financial system was on the verge of collapse. As the result of his efforts, and the efforts of Joe Biden, against unprecedented... Republican obstructionism, we have made enormous progress."

The Vermont senator, fresh off his landslide victory in New Hampshire's first-in-the-nation primary, continued to denounce Clinton's criticism.

"You know what, last I heard, we live in a democratic society. Last I heard, a U.S. senator has the right to disagree with a president, including a president who has done such an extraordinary job," Sanders said. "So I have voiced criticisms – you're right. [But] President Obama and I are friends, I have worked for his first election and his reelection, [and] I think it is really unfair to suggest I have not been supportive of the president. I have been a strong ally on virtually every issue."

"Do senators have the right to disagree with a president? Have you ever disagreed with a president? I suspect you have," he said.