2020 Democratic presidential front-runner Joe Biden mocked Bernie Sanders for his rhetoric of "revolution" at a Washington, D.C., campaign event.

In a rambling answer in which he appeared to advocate a middle way between helplessness and overthrowing the system.

"You try to persuade. Doesn't mean you can do it all the time," said Biden, 76. "If you start off with the notion there is nothing you can do, well then why don't you go all go home then, man? Or let's start a real, physical revolution if you are talking about it because we have to be able to change what we are doing within our system."



Biden's comment came in an answer to a question from MSNBC's Joy Reid about how he believed he could work with congressional Republicans should he win the White House in 2020.

Sanders, 77, who is running second in most Democratic primary polls, called last week for a "political revolution." His 2017 book Bernie Sanders Guide to Political Revolution made him a millionaire.

[ Read more: Biden vows to campaign more in the South, says he will win South Carolina and other states]