Democratic presidential candidates Hillary Clinton and Bernie Sanders clashed sharply in a debate on Thursday over their support for President Barack Obama, with Sanders accusing Clinton of "a low blow" after she compared him to Republicans.

As the Democratic race moves to states with large minority populations, both candidates openly courted black and Hispanic votes during a debate that was far more restrained and cordial than last week's contentious debate in New Hampshire.

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In the sharpest exchange of the night, Clinton attacked Sanders for being too critical of Obama, who is extremely popular with the black voters who will play a big role in the outcome in South Carolina and other upcoming nominating contests.

"The kind of criticism that we've heard from Sen. Sanders about our president, I expect from Republicans, I do not expect from someone running for the Democratic nomination to succeed President Obama," said Clinton, who served as secretary of state during Obama's first term.

"Madam Secretary, that is a low blow," said Sanders, a U.S. senator from Vermont. Sanders said he had been an Obama ally in the Senate even if he did not always agree with him.

"Do senators have the right to disagree with the president?" Sanders asked.

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Clinton, who has eagerly embraced Obama's legacy, said Sanders had called Obama weak and a disappointment, and "that goes further than saying we have our disagreements."

With Clinton looking to rebound after her crushing 22-point loss to Sanders in the New Hampshire primary on Tuesday, the two also differed over health care and Wall Street.

Even so, the restrained exchange on Thursday was unlikely to change the trajectory of a race that has intensified dramatically over two weeks.

Clinton accused Sanders of misleading Americans on his health care. She said his proposal for a single-payer, Medicare-for-all health care plan would mean dismantling the program known as Obamacare and triggering another intense political struggle.

"Based on every analysis I can find by people who are sympathetic to the goal, the numbers don’t add up," Clinton told Sanders. "That's a promise that cannot be kept."

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Sanders said he was simply moving to provide what most industrialized countries have – health care coverage for all.

"We're not going to dismantle anything," Sanders said. "In my view, health care is a right of all people, not a privilege, and I will fight for that."

Sanders also repeated his accusation that Clinton is too beholden to the Wall Street interests she once represented as a U.S. senator from New York, noting her Super PAC received $15 million in donations from Wall Street.

"Let's not insult the intelligence of the American people," he said. "Why in God's name does Wall Street make huge campaign contributions? I guess just for the fun of it – they want to throw money around."