The drummer has long been a fan of the Democrat, after previously campaigning to help him win a seat in the U.S. Senate in 2006, and he recently lent his voice to a campaign video for the Vermont Senator's race for the White House.
Now Fishman has dedicated more time to help Sanders win the Democratic nomination by teaming up with the Kenya Hall Band to perform for fellow demonstrators at a rally in Portland, Maine, where he also addressed the audience.
His support won him a special shout-out from the presidential wannabe, who went on to hail Phish for their musical legacy.
"Let me thank one of Vermont's heroes who is now transplanted: Jon Fishman," Sanders said. "Jon and Phish have made New England proud. They are one of the great bands, have been one of the great bands in this country, so Jon, we thank you very much."
The musician isn't the only celebrity to stump for Sanders - filmmaker Spike Lee, rockers Vampire Weekend, and rapper Killer Mike are among those who are backing the 74-year-old to beat main competitor Hillary Clinton for the party's nomination.
The Maine rally took place a day after initial polling for the so-called Super Tuesday (01Mar16) indicated Clinton would win against Sanders in seven of the 11 states polled if voters were to cast their ballots now. Among Clinton's big wins included Virginia, Georgia, Texas, and Massachusetts, while Sanders triumphed in his home state of Vermont, Oklahoma, Minnesota and Colorado.