Two days before the fifth Democratic primary debate, hosted by MSNBC, four Democratic presidential hopefuls called on the Democratic National Committee (DNC) to demand Comcast, MSNBC's parent company, commit to conducting an independent investigation into the company's "toxic culture" that allowed the sexual harassment and abuse of staffers.

Senators Cory Booker, Kamala Harris, Bernie Sanders, and Elizabeth Warren sent a letter to DNC Chairman Tom Perez on Tuesday ramping up the pressure on the party to reiterate its support for victims of sexual misconduct.

"We, the undersigned candidates, are very concerned about the message it would send to sexual assault survivors if our next debate is sponsored by MSNBC without clear commitments from Comcast, the parent company of NBC and MSNBC, to conduct an independent investigation into the toxic culture that enabled abusers and silenced survivors," the 2020 hopefuls wrote. None of the candidates have threatened to withdraw from the debate.

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Democratic presidential candidates are set to take the stage Wednesday night for the fifth debate of the 2020 campaign. The event is co-hosted by MSNBC, NBC's sister network, and the Washington Post, and will feature an all-female panel of moderators.

NBC has come under scrutiny for its handling of allegations of sexual misconduct leveled against former "Today" co-host Matt Lauer, who was fired from the network in 2017 after an employee accused him of "inappropriate sexual behavior in the workplace."

The woman, Brooke Nevils, told reporter Ronan Farrow in his book "Catch and Kill" that Lauer raped her in a hotel room during the 2014 Winter Olympics in Sochi, Russia. An internal review conducted by NBCUniversal last year found network executives were unaware of the allegations against Lauer until late 2017 when four women accused him of sexual misconduct. Lauer has claimed the encounter was consensual.

Farrow also claimed NBC refused to air his reporting on Hollywood producer Harvey Weinstein, who was accused by numerous women of sexual misconduct.

Despite the fact that an internal investigation at NBC found that company executives weren't at fault due to a lack of formal complaints, the presidential contenders wrote, "there is clearly something wrong with a work environment" that hesitates to hold its management accountable. "That's what allowed the behavior of powerful abusers inside the company to go unchecked," the group added.

In October, after Farrow's book was published, NBC told the Hollywood Reporter that no additional investigation would be launched

"Donald Trump has been credibly accused of sexual harassment and sexual abuse by dozens of women," the Democrats told Perez. "We, as a party, have to offer voters a clear and unquestionable difference come November when it comes to these important issues. We cannot do that when we prop up and support companies that have systematically covered up numerous incidents of sexual violence with no accountability or changes in leadership."

Sanders and Warren are among the leading candidates vying for the Democratic presidential nomination. Ten 2020 Democrats will appear on stage at the debate in Atlanta.