(CNN) Sen. Bernie Sanders "wants to make sure that Trump is beaten in 2020," according to his 2016 campaign manager, Jeff Weaver.

Weaver, the author of "How Bernie Won: Inside the Revolution That's Taking Back Our Country -- and Where We Go from Here," said that Sanders, a Vermont independent, will run in 2020 only if "he's the person who's best able to do that."

And what does Sanders' former campaign manager think?

"I'm very clear about what I think he should do," Weaver told David Axelrod on "The Axe Files," a podcast from The University of Chicago Institute of Politics and CNN.

The last three words of his book are "Run, Bernie, run."

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