“She should be removed,” said Ms. Crowell, of Tustin, Calif., who attended a Sanders rally here on Tuesday and said she planned to vote for a third-party candidate if Mr. Sanders failed to overtake Mrs. Clinton and capture the Democratic nomination. “I don’t know why she’s not already being told, ‘You can’t run because you’re being investigated.’ I don’t know how that’s not a thing.”

Campaigning in California, where polls show a tightening primary race, Mr. Sanders continued to hit Mrs. Clinton over her positions on Wall Street, trade deals, the minimum wage, hydrofracking and “super PACs” — seemingly everything except her emails, which he famously took off the table as an issue during an early Democratic debate. But Mrs. Clinton faces renewed criticism after an inspector general’s report faulted her for violating the State Department’s records-retention policy. And as the F.B.I. continues its investigation into the handling of classified information, attendees at Sanders rallies have repeatedly expressed hope that the scandal would result in criminal charges against Mrs. Clinton.

“If there’s any chance of her getting indicted, they shouldn’t even consider her for the nomination,” said Zachary O’Neill, 21, of Escondido. “We can’t have a criminal in the White House.”

And what would be a more colossal comeuppance to the Democratic establishment?