WAPO: Sanders wants Democrats to think that Warren's gains are a function of moderates. They aren't. [View all]
In Monmouths April poll, Warren was running fifth, with 6 percent of poll respondents identifying her as their preferred candidate. In the new poll, she and Sanders are essentially tied.
Shortly before that poll came out, Sanderss campaign lifted up a report from Politico that seemed as though it might help explain Warrens improved position: She was gaining support from what Sanders called the corporate wing of the Democratic Party. Which is to say the partys more moderate, less progressive arm, the segment of the party that, in Sanderss framing, will pull out all the stops to curtail his economic revolution.

It doesnt take much reading between the lines here to understand Sanderss argument: Centrists are circling around Warren (per Politico) because they are afraid of legitimate progressive positions like his own.
Patrick Murray, who runs the Monmouth University Polling Institute, noted on Twitter that the Politico article relied on the opinions of a few people in determining that more-moderate Democrats were lining up behind Warren. One, for example, was the co-founder of a centrist think tank that, Politicos Natasha Korecki and Charlie Mahtesian write, is learning to live with Warren.
Murray noted that Monmouths polling paints a different picture than Politicos interviews would suggest.

https://www.washingtonpost.com/politics/2019/06/19/sanders-wants-democrats-think-that-warrens-gains-are-function-moderates-they-arent/?utm_term=.15c7825c7015