Joe Biden's failure to inspire Bernie Sanders supporters could lead to his defeat by Donald Trump in November, a senior adviser to the Bernie campaign has warned.
In a blog post published to Medium on Friday, the "America's Promise PAC" said there is a "clear and dangerous trend" that could keep the Democrats from the White House.
America's Promise was launched by Jeff Weaver, Mr Sanders's former campaign manager. He said a significant portion of Bernie Sanders supporters were "currently unsupportive and unenthusiastic" about the Biden candidacy.
"If all of Sanders' base turned out for Joe Biden in November, he could defeat Trump and take back the White House for Democrats. Here's the problem: significant portions don't currently plan to," Mr Weaver wrote.