To witness one of Bernie Sanders’s Fighting Oligarchy tour stops, which rolled through Nevada, Colorado and Arizona this weekend, is to stumble through time.

It’s 2025, but when Mr. Sanders, the senior senator from Vermont, delivers lines, in his still-intact Brooklyn drawl, about “millionaires and billionaires” and the 1 percent keeping the working class underfoot, it could be 2015, or 2005. Even further back than that, perhaps.

It is not merely Mr. Sanders’s speech. At 83, his image is unmoving — even if his hairline sits a bit further back than it used to. He wears, as he has for years, wire frames no fancier than the ones you’d find in the drugstore checkout line, unremarkable navy suits and cornflower blue dress shirts. His younger sparring partners in the Democratic Party — Barack Obama, Pete Buttigieg, Gavin Newsom, among them — long ago shed their sport coats to stump in shirt sleeves. Not Bernie. Like an aging accountant, his blazer stays on.

The out-of-time feeling extends beyond the stage at the Fighting Oligarchy tour. The crowds that fill these whistle stops (which Mr. Sanders has said are the among the largest of his political career) wear “Bernie 2016” T-shirts and “Bernie 2020” caps — dusted off keepsakes of Mr. Sanders’s prior presidential runs, but also reminders that he has been a Democratic bridesmaid for longer than some in his crowd have been able to vote.

The swelling masses Mr. Sanders is drawing in states that often went for Donald J. Trump in the last election reflect how a cohort of Democrats are once again turning to Mr. Sanders as the broader party seems incapable of chipping away at President Trump’s authority. (Though he’s previously run to be the Democratic presidential candidate, Mr. Sanders is an independent and has lately pushed others to follow him. Still, Mr. Sanders’s enduring appeal to left-leaning Democrats, in terms of outright fandom, can feel similar to Mr. Trump’s hold over Republicans.)

The political sands have shifted since Mr. Sanders last made a run at the presidency. Around a decade ago, could anyone pick out Pete Hegseth, let alone his tattoos? Back then, Elon Musk was an electric-car entrepreneur, not the government’s cost cutter in chief. Paul Ryan was speaker of the House in 2016 — remember him? But Mr. Sanders, with his eat-the-rich message, is a constant.

And today, while Democrats on the Hill squabble over budget votes and polls show their appeal sinking with voters, the same-as-he-ever-was Mr. Sanders is barnstorming the country along with Alexandria Ocasio-Cortez, the congresswoman from New York, drawing crowds as if they were The Grateful Dead, or their successors, Dead & Company.

Indeed, the Vermont independent is, in so many ways, the Grateful Dead of American politics. Like the Dead, he has a steadfast fan base — both groups are now often as white-haired as he is — that hangs on every new interpolation of an old hit. (Mr. Sanders’s working shots at Mr. Musk into his speech is his version of the Dead retooling “Casey Jones.”) And he also continues to find purchase with a younger generation, drawn into his anti-corporate messaging, which continues to echo the youth-centric Occupy Wall Street movement of the aughts.

On the Fighting Oligarchy tour, it could be said that Ms. Ocasio-Cortez, in her tucked white shirts and leopard-print flats, is playing a similar role to John Mayer’s, who started touring with Dead & Company in recent years — an acolyte with her own sizable fan base, adding a jolt to the proceedings.

And the crowds: Like Deadheads, Bernie’s true believers love the merch. Today, you can buy “Bernie was Right” tees, shirts that style a photo of a young Mr. Sanders bordered by the phrase “Rage Against the Machine” and tees praising the irascible statesman in Spanish as “Tío Bernie.”

Mr. Sanders’s site continues to sell what it has deemed the “Bernie Classic Logo” tees, with his name in the recognizable font that he has used since at least his 2016 presidential run. Those run $27.

While the camo “Harris Walz” hats that were coveted during Kamala Harris’s recent presidential run are a scarcity, Bernie hats were visible at his rally in Colorado, as were shirts with his name and buttons depicting his trademark glasses and flecked white hair — reflections of how the aging politician maintains a pop cultural cool that has recently eluded Democratic politicians.

How far that can take him (or for that matter, Ms. Ocasio-Cortez, who draws her own A.O.C.-teed supporters) is an open question. After all, the Grateful Dead is still considered a cult band.