The Democratic National Committee sent out an email to the 2020 Democratic presidential campaigns reminding them not to use "foul language" in the upcoming Democratic debate this Thursday.

The email, obtained by CNN and Axios, reminded candidates that the debate, hosted by ABC News, will be pursuant to Federal Communications Commission regulations that fine networks for excessive swearing on air.

Former Rep. Beto O'Rourke of Texas, in particular, is known for his liberal use of the F-bomb, so much so that it even became the subject of an attack ad against him during his 2018 Senate run in Texas.

In recent weeks, O'Rourke has employed the four-letter-word in the context of discussing gun violence after two deadly mass shootings took place in El Paso and Odessa, Texas.

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The Democratic National Committee sent out an email to the 2020 Democratic presidential campaigns reminding them not to use "foul language" in the upcoming Democratic debate set for Thursday, September 12 in Houston.

The email, obtained by CNN and Axios, reminded candidates that the debate, hosted by ABC News, will be pursuant to Federal Communications Commission regulations that fine networks for excessive swearing on air.

"We will not be broadcasting on any delay, so there will be no opportunity to edit out foul language," the email said. "Candidates should, therefore, avoid cursing or expletives in accordance with federal law and FCC guidelines."

Read more: Here's who will be onstage for the September Democratic debate hosted by ABC, what time it'll start, and how to watch

The DNC's previous debate partners, MSNBC and CNN, are not subject to the same FCC guidelines and did not send out a similar reminder before their respective debates in June and July, according to CNN.

It used to be extremely unusual and taboo for politicians — much less presidential candidates — to openly curse. But with his penchant for demeaning and insulting opponents, President Donald Trump has drastically changed the norms of what is acceptable behavior for politicians.

Former Rep. Beto O'Rourke of Texas, in particular, is known for his liberal use of the F-bomb, so much so that it even became the subject of an attack ad against him during his 2018 Senate run in Texas.

In recent weeks, O'Rourke has employed the four-letter-word in the context of discussing gun violence and what he perceives as dangerous inaction by the Republican Party.

This summer, Texas experienced a mass shooting that killed 21 people in El Paso — O'Rourke's hometown — on August 3 and another shooting spree in Odessa that killed eight people and injured two dozen others on August 31.

In the wake of the El Paso shooting — which is being prosecuted as an act of domestic terrorism — O'Rourke became frustrated when a reporter asked him if there was anything Trump could do to make the situation better.

"What do you think? You know the s--- he's been saying. He's been calling Mexican immigrants rapists and criminals. I don't know, like members of the press, what the f---? Hold on a second, you know, I ... it's these questions that you know the answers to," O'Rourke admonished.

Read more: 'You know the s--- he's been saying': Beto O'Rourke criticized the media's coverage of Trump in the wake of a mass shooting in El Paso

And after the Odessa shooting, O'Rourke again used the word on CNN, saying, "We're averaging about 300 mass shootings a year. No other country comes close. So yes, this is f--- up."

Other presidential candidates, including Sen. Cory Booker and Rep. Tim Ryan, have also described gun violence in America and the lack of a substantive Republican response as "bulls---" and told the GOP to "get their s--- together on the issue."

And former presidential candidate Sen. Kirsten Gillibrand of New York found herself in hot water for saying "if we're not helping people, we should go the f--- home" back in the summer of 2017.

O'Rourke argues that criticism of his swearing is a distraction from the real issues, saying, "profanity is not the f-bomb. Profanity is a 17-month old baby being shot in the face," quoting a rabbi's rival tweet. "Let's speak clearly, and bluntly, and use decisive language."