DES MOINES, Iowa — With tensions rising between 2020 Democratic rivals Bernie Sanders and Elizabeth Warren, what started as a good week for Joe Biden could get better.

On Sunday, reports surfaced that the Sanders campaign had been instructing its staffers to tell Iowa Democrats that Massachusetts Sen. Warren was incapable of building a broad coalition of voters to beat President Trump in a general election. Warren, 70, responded by saying she was “disappointed to hear that Bernie is sending his volunteers out to trash me.”