Hillary Clinton Hillary Diane Rodham ClintonHillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters FBI chief says Russia is trying to interfere in election to undermine Biden MORE accused Bernie Sanders Bernie SandersMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters Why Democrats must confront extreme left wing incitement to violence MORE of criticizing Presidents Obama and Bill Clinton William (Bill) Jefferson ClintonD-Day for Trump: September 29 Trump job approval locked at 42 percent: Gallup If Trump doesn't know why he should be president again, how can voters? MORE because "he wasn't really a Democrat until he decided to run for president."

Responding to Sanders's criticism of her husband's administration, she defended his economic record while pivoting to a common charge from her campaign about how Sanders has also been critical of Obama.

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"I know that Sen. Sanders has also attacked President Obama. He called him weak, called him disappointing, tried to get someone to run against him [in a primary in 2012]," she said during MSNBC's Democratic presidential forum in Nevada two days before the state's caucus.

"Maybe it’s that Sen. Sanders wasn't really a Democrat until he decided to run for president, so he doesn't really know what the past two Democratic presidents did." Sanders, an Independent senator from Vermont, calls himself a democratic socialist.

The crowd, a mix of Clinton and Sanders supporters as well as undecided voters, responded with a mix of cheers and boos.

"You know it's true," Clinton told the crowd.

When MSNBC's moderators noted that both candidates had been jeered at some point over the night, Clinton responded, "The facts are our friends, so let's talk about them."

Sanders is the longest-serving Independent lawmaker in Congress. While he's caucused with the Democrats, he never identified as a member of the party until his presidential bid.

The Clinton campaign doubled down in a statement from communications director Jennifer Palmieri released just minutes after the forum ended.

"If Senator Sanders wants to be the standard bearer of the Democratic Party, he should spend less time attempting to tear down the very real accomplishments of two of the most successful presidencies in modern times," the statement said.

"Their records of accomplishing tangible, life changing results for the American people speak for themselves."