Sen. Bernie Sanders (I-VT) just cannot catch a break from his top competitors for the 2020 Democratic presidential nomination. After former Vice President Joe Biden compared his more motivated supporters — the so-called “Bernie Bros” — to President Donald Trump, Sen. Elizabeth Warren (D-MA), who must win Nevada in order to justify staying in the race, called the Vermont socialist’s supporters a “foundation of hate” Tuesday.

Sanders, Warren told NBC News, “has a lot of questions to answer” over why his supporters have responded so viciously to supporters of other candidates, online and, more recently, in person — particularly in Nevada, where the next Democratic caucus is slated to be held February 22nd.

“I’ve said before that we are all responsible for what our supporters do, and I think Bernie has a lot of questions to answer here,” Warren told reporters. “I am particularly worried about what happened in the attacks on members of the culinary union, particularly on the women in leadership.”

“The whole notion of publishing their personal addresses, their phone numbers, and then making very aggressive threats against their own safety and the safety of their families,” Warren added, referencing how Sanders’ supporters treated members of the Nevada Culinary Union, which refused to endorse a Democratic candidate last week. “That is not how we build an inclusive Democratic Party. We do not build on a foundation of hate.”

Those are stong words from the Massachusetts Senator who, up until last month, when she began sinking in the polls in earnest, had tried to forge a bridge between her own campaign and Sanders’. In January, though, Warren became aggressive against the Vermont socialist after allegedly discovering that Sanders volunteers were cautioning likely voters against casting a ballot for her in the primaries and after it emerged that Sanders had expressed reservations about the success of a Warren presidential campaign against President Donald Trump.

Rumors were, initially, that Sanders had said a woman “can’t win” the White House. Warren acknowledged the rumor but clarified that Sanders was referring to her — and the 2020 elections — specifically. Sanders supporters defended the remarks, noting Hillary Clinton’s failed 2016 presidential campaign, and linking Clinton’s inability to secure the presidency to institutionalized sexism.

Sanders, as noted before, has found no need to apologize for the behavior of his supporters, saying only that “[a]nybody making personal attacks against anybody else in my name is not part of my movement,”even though the “Bernie Bros” have since taken their aggressive movement offline, engaging in near violent behavior just last weekend after 60 Sanders delegates were disqualified from voting by the Nevada Democratic party at its annual convention in Las Vegas.

In response to harsh words from Biden over the weekend, Sanders referenced violence against his own campaign — shots fired into his campaign office late last year, though details on that incident are scarce, and its not clear whether the single bullet hole found in the wall of Sanders’ office in northwest Las Vegas, was from a politically motivated attack, per the Las Vegas Sun.

Both Biden and Warren are, of course, looking for any excuse to sway voters against Sanders’ bid for the 2020 Democratic presidential nomination — a bid he now looks to be in danger of winning, given his success in Iowa and New Hampshire, and his poll numbers in Nevada, South Carolina, California, and Texas, four of the biggest states doling out delegates to the DNC in the coming weeks.