“Some call it the ‘my way or the highway’ approach to politics,” Mr. Biden, the former vice president, wrote in a Medium post. “But it’s worse than that. It’s condescending to the millions of Democrats who have a different view. It’s representative of an elitism that working and middle-class people do not share: ‘We know best; you know nothing.’ ‘If you were only as smart as I am you would agree with me.’ This is no way to get anything done.”…

In several venues on Tuesday, Mr. Biden also repeatedly seized on the fact that Ms. Warren was once a registered Republican, though she is now a leading progressive contender for the Democratic nomination and Mr. Biden is perceived by many on the left as too moderate and overly focused on striking deals with Republicans.

“I have fought for the Democratic Party my whole career,” Mr. Biden wrote. “I know what we stand for, who we stand with and what we believe. And it’s not just policies or issues. It’s in my bones. That’s not something everyone in this primary can say.”

He was more explicit at the fund-raiser: “I’ve been a Democrat my whole life. This person has only fairly recently in the mid-’90s become a Democrat.”