Sean McElwee, a Biden critic who founded the left-wing think tank Data for Progress, said Biden’s path in the 2020 Democratic primary has proven to be like Donald Trump’s in the 2016 GOP contest.

“No one is treating him as what he has been for the entirety of the race, the front-runner. There’s sort of always been an assumption that he’s going to collapse,” he said.

Both Biden and Trump were written off by both rival campaigns and many opinion leaders in their own parties, such as donors, strategists and ideological columnists, despite consistently leading in the polls. And both have a connection to their base that is more personal, making them somewhat impervious to criticism about their ideological purity or consistency.

“Joe Biden has influence among a certain segment of the Democratic primary electorate, and very few people are making arguments that are going to be persuasive to those voters,” McElwee said. “Progressives shot all their shots right at the beginning and then were like: ‘I guess that didn’t work. We’ll just fight each other and then deal with him later.'”