Every candidate faces voter bias, the senator said while addressing a conversation he allegedly had with Elizabeth Warren in 2018.
The Democratic candidates disagreed without getting into any big fights at the final debate before the Iowa caucuses.
Sanders denied the alleged 2018 exchange, and Warren has yet to comment.
In an email, Harris said her campaign doesn't have the financial resources to continue.
"Bernie's not a Democrat," one close adviser to the former president told Politico.
More than a dozen presidential candidates addressed 13,000-plus Democratic activists, volunteers and supporters in downtown Des Moines.
The New York congresswoman's endorsement provides a jolt of energy to a presidential campaign seeking to regain momentum.
The New York Times reports the video shows a fake Trump attacking versions of PBS and HuffPost, as well as a fake Bernie Sanders.
Riggs, a neuropsychologist and mom of three, died two days after being diagnosed with neuroendocrine cancer, according to her obituary.
The campaign said Senator Sanders "will be resting up over the next few days."