The president’s observations on the state of the race come after POLITICO reported Saturday that Sanders’ campaign had begun attacking Warren as a candidate with a “highly-educated, more affluent” bloc of support who is “bringing no new bases into the Democratic Party,” according to a set of talking points distributed to Sanders volunteers.

Warren hit back at Sanders on Sunday, remarking that she hopes he “turns his campaign in a different direction” and warning against “the impact of the factionalism” that plagued Democrats in the previous presidential election.

“I was disappointed to hear that Bernie is sending his volunteers out to trash me,” she said following a town hall in Iowa. “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 movement we’re trying to build.”

Sanders and Warren, both senators who have championed contentious policy proposals over the course of the nominating contest, have largely refrained from targeting one another as they compete for the support of liberal voters.

But the long-simmering tensions between their campaigns have burst into public view with just three weeks to go until the Iowa caucuses, as Sanders has consolidated the party’s left wing and emerged as the chief challenger to the more moderate Joe Biden.