If Democratic presidential front-runner Hillary Clinton were to lose next week's California primary by a wide margin, there could be room for Vice President Joe Biden to make a bid for the nomination, said Walter Isaacson, former CNN chief and TIME magazine editor.
Under that scenario, Biden would have a 20 percent chance, Isaacson told CNBC's "Squawk Box" on Thursday, saying he also could see as an outside possibility 2004 Democratic presidential nominee John Kerry, who succeeded Clinton as President Barack Obama's secretary of state.
Biden, after much consideration, decided in October not to run for the White House again. The vice president, along with Clinton, ran for the nomination in 2008. They both lost out to Obama, who later chose Biden as his running mate.
"If Hillary Clinton loses California in a serious way, it shows she's not connecting with the tenor of the times, especially people's frustration and anger," said Isaacson.
"Sanders can't win. But could you have a fall back ... a Joe Biden or maybe a Kerry? But I think Joe Biden is more likely. That's a 1-in-5 shot," said Isaacson, currently CEO of the Washington, D.C.-based Aspen Institute think tank.
"Whatever you may think of Biden, he connects more," Isaacson said. "He's really [a] decent and honorable guy."
While the final Democratic contest comes on June 14, when the District of Columbia holds its primary, this coming Tuesday basically marks the conclusion of the race. That's when California's 546 delegates are up for grabs. Among the other five June 7 races, New Jersey has the second-largest delegate haul of 142.
Including super delegates, who are free to support any candidate, Clinton is just shy of the 2,383 delegates needed to clinch the Democratic nomination. Sander has just 1,543 delegates, despite winning 11 out of the last 18 contests.
Besides political commentary, Isaacson is also well-known for the 2011 "Steve Jobs" biography of the Apple co-founder.