The big picture: President Biden, who was mentored by Mondale through the years, said in 2015 that the former vice president gave him a "roadmap" to successfully take on the job.

-He was the first vice president to have an office in the White House and was deeply engaged in both U.S. and foreign policy, working closely with the president.

-"I took Fritz's roadmap. He actually gave me a memo, classic Fritz, gave me a memo, as to what I should be looking for and what kind of commitments I should get to be able to do the job the way Fritz thought it should be done," Biden said at an event honoring Mondale in 2015.

Backstory: Mondale spoke by phone on Sunday with President Biden and former Presidents Jimmy Carter and Bill Clinton, as well as Vice President Harris and Minnesota Gov. Tim Walz, said his friend and former campaign staffer Tom Cosgrove. While he and his family believed his death was imminent, after those calls he "perked up."