Presidential contenders Bernie Sanders and Elizabeth Warren have had a bit of a dustup. The two Democratic presidential candidates representing the party’s left wing in the 2020 race found themselves at odds this weekend after Warren responded to a call script for volunteers that was reportedly issued by the Sanders campaign. The entire episode is a lesson in the growing friction in the Democratic presidential primary — and a telling example of just how ridiculous and bitter things may get.

It all started with a report by Politico, which included written guidelines for Sanders volunteers calling potential voters who might support other candidates. In the script, Sanders volunteers are reportedly advised to characterize Warren supporters as highly educated and affluent.

“I like Elizabeth Warren. [optional],” the script begins, according to Politico. “In fact, she’s my second choice. But here’s my concern about her.” The script then questions Warren’s ability to get elected based on her base’s demographics, reading, “People who support her are highly educated, more affluent people who are going to show up and vote Democratic no matter what” and “She's bringing no new bases into the Democratic Party.”

“We need to turn out disaffected working-class voters if we’re going to beat Trump,” the script’s section on Warren concludes. In a section apparently about “status quo candidates,” the document also mentions the lack of enthusiasm around former vice president Joe Biden’s campaign and the low support among young and African-American voters for Pete Buttigieg, the former mayor of South Bend, Indiana.

According to Politico, the Sanders campaign did not deny the script’s authenticity. Politico reporter Alex Thompson took to Twitter to deny claims from Sanders supporters that the script was uploaded by a volunteer and not an official campaign document, writing that the document had “Paid for by Bernie 2020” written on it.

Warren responded to the script on Sunday, telling reporters, “I was disappointed to hear that Bernie is sending his volunteers out to trash me. Bernie knows me and has known me for a long time. He knows who I am, where I come from, what I have worked on and fought for, and the coalition and grassroots movements we’re trying to build.”

“Democrats want to win in 2020,” Warren continued. “We all saw the impact of the factionalism in 2016, and we can’t have a repeat of that. Democrats need to unite our party, and that means pulling in all parts of the Democratic coalition.”