Bernie Sanders found himself on the receiving end of attacks from both President Donald Trump and Elizabeth Warren on Sunday, a reflection of his rising status in the Democratic presidential race and perceived momentum just three weeks out from the Iowa caucuses.

In a tweet, Trump declared, “Wow! Crazy Bernie Sanders is surging in the polls, looking very good against his opponents in the Do Nothing Party. So what does this all mean? Stay tuned!” Sanders responded in the same medium: “It means you’re going to lose.”

But it was Warren — who has generally avoided criticizing her fellow progressive over the course of the Democratic primary — who offered the sharpest criticism of the Vermont senator, saying she was “disappointed” by a report that the Sanders’ campaign is instructing its volunteers to speak negatively about her to win over undecided voters and suggesting he is too divisive to beat Trump.

“We cannot nominate someone who takes big chunks of the Democratic coalition for granted. We need someone who will bring our party together,” she told reporters after a campaign event in Iowa.

“We need someone who will excite every part of the Democratic Party, someone who will be there, someone that every Democrat can believe in.”

Warren also warned against repeating “the factionalism of 2016,” during which the unexpected strength of Sanders’ challenge to Hillary Clinton’s candidacy produced a drawn-out and oftentimes nasty Democratic primary fight that some Democrats say contributed to Trump’s win.

Her comments come in response to a report in Politico revealing the Sanders campaign canvassing script suggests volunteers tell voters leaning towards Warren that “people who support her are highly-educated, more affluent people who are going to show up and vote Democratic no matter what” and that the senator is “bringing no new bases into the Democratic Party.”

The Warren campaign cited the Politico report in a fundraising appeal Sunday night.

Both Sanders and Warren, who are vying for the progressive lane in the primary and largely agree on many of the biggest issues in the race, have up until now publicly avoided attacking one another and in fact have been complimentary of each other.

In contrast, Sanders has in recent weeks been going aggressively after opponent Joe Biden for his support for the Iraq War and his trade policy.

While Biden has largely stayed mum on Sanders’ attacks in recent days, Warren’s broadside sets the potential for a debate-stage clash in which he’ll likely be attacked by multiple opponents. The Vermont senator has been rising in a handful of state and national polls over the past month and is seen to have momentum heading into the final three weeks before the first nominating contest takes place in Iowa.