"The memos that Comey leaked were created on a Federal Bureau of Investigation computer while he was the director", Sanders said during Wednesday's briefing.
"There certainly was communication and there certainly was an understanding of some sort", she said.
Sanders was asked in Tuesday's White House press briefing.
"I can't think of a single time where he made a deal with anyone from the opposite side, from beyond the Democrat Party". At a campaign event past year, Clinton said half of Trump's supporters belong in a "basket of deplorables".
Sanders' remarks come one day after she suggested the possibility of Comey lying during his sworn testimony before Congress about his time working for Trump.
Clinton has been promoting the book, entitled What Happened, over the past week.
Water level rising rapidly in Naples, Marco Island, Florida
Now, evacuated Floridians are sitting in bumper-to-bumper traffic to head home and face monumental cleanups throughout the state. Key West is a popular tourist destination, drawing revelers to the Duval Street bars where pianos duel and frozen drinks flow.
President Donald Trump plans to visit storm-stricken Florida on Thursday, the White House said, his third such trip to a weather devastated state after a spate of violent USA weather.
Sanders has been hammering Comey all week, arguing the Department of Justice should consider prosecuting him for his actions.
"I think there's no secret Comey, by his own self-admission, leaked privileged government information".
The president has said he's simply doing "what the people of the United States want to see".
Clinton recalled in her book that it felt as though Trump was "literally breathing down my neck" as he lurked behind her during the debate in St. Louis.