The dangerous silence from Warren and progressive officials across the country comes at the worst time for Sanders, who’s suddenly losing momentum in a two-man race with the former vice president as another set of high-stakes primary elections looms. Sanders is moving forward with the same coalition that was beaten soundly earlier this week. And if he cannot find a way to grow, and grow quickly, the Vermont senator’s 2020 challenge will only become more dire.

There is an increasing sense of frustration within Sanders’ campaign, where a divide over strategy has emerged between opposing camps, according to a person close to the campaign who spoke on condition of anonymity to disclose private discussions.

On one side, campaign manager Faiz Shakir wants to empower the pool of existing supporters, such as progressive congresswomen Alexandria Ocasio-Cortez and Rashida Tlaib, because of their organic appeal to voters. On the other, senior adviser Jeff Weaver is pushing for a wider range of endorsements to broaden Sanders’ coalition.

Within the campaign, some lament Sanders’ unwillingness to court elected officials as Biden’s coalition grows exponentially.