Both on the record and on background, on Twitter and on cable television, Clinton’s former aides and allies are taking pains to lay out what they see as all of Sanders’s flaws, imperfections and vulnerabilities — much as he once did to their ex-boss during a primary that saw mud flying on both sides.

“I would say — and for all I know, the Sanders people might take this as a compliment — among a lot of the major donors in the party, there’s concern that he could emerge,” said David Brock, a longtime Clinton ally who founded a pro-Clinton super PAC in the 2016 campaign and later authored a public apology to Sanders for some of his bare-knuckled criticisms during the primary. “There are some very dyed-in-the-wool Democrats that wouldn’t at all be enthusiastic about supporting him in a general election.”…

In recent weeks, former Clinton aides have blasted Sanders for everything from his policy record to his campaign kickoff speech to the composition of his small-dollar donors. The attacks come as Sanders is in the midst of a successful rollout, raising $10 million less than a week into his 2020 candidacy and attracting a combined 25,000-plus people to his first two kickoff rallies.

When Sanders pulled in $1 million in the first three-and-a-half hours of his campaign, Adam Parkhomenko, the former director of grassroots engagement for the 2016 Clinton campaign, tweeted, “Only half were named Vladimir.”