In a political season when some of the Democrats considering presidential runs have been unusually direct about their ambitions, the independent senator from Vermont's next steps remain a genuine mystery - including, it sometimes seems, to himself.

Sanders tries his best to avoid talking about it now, so close to a midterm election the party is so desperate to conquer. Listening to the question, in its manifold formulations, can at times appear to physically pain him. But his work and itinerary this fall, as he travels to boost Democrats around the country while continuing to grow and sustain the grassroots movement he elevated with his 2016 campaign, has guaranteed its asking.

The last time around, this process played out in lower velocity settings. No one was bellowing "Ruuuuun" when, as a frequent guest on liberal Bill Moyers' public television program, Sanders mused a bit more freely about the prospect. During an appearance in October of 2014, after some friendly nudges from Moyers, he set the bar for a 2016 bid.

"The main issue that I'm trying to figure out, and I'm going around the country talking to people -- is there support for a candidacy which is really prepared to take on the billionaire class?" Sanders said. "Can you do it? How do you do it? How do you get the resources to do it? How do you build the grassroots organization?"

Four years on, the answers are clear, and if the standard now were roughly the same, a second consecutive swing would be a no-brainer.

Sanders' grassroots following on the political left is unparalleled in Democratic politics. Anger and a desire to act against the influence of the wealthy few is embedded in both American political life and increasingly, the popular culture.

Small dollar donors across the country are swelling liberal candidates' campaign accounts, much as they ended up doing for Sanders in 2016. Some of his signature policies and, perhaps as importantly, his political language, have been adopted by a wide range of Democrats. The party this midterm season has been mostly focused and largely coherent in its pledges to expand health care and root out corporate influence from Capitol Hill to state legislatures and city councils.

But as former campaign manager Jeff Weaver readily acknowledged in an interview outside a Sioux City, Iowa, rally with J.D. Scholten, the Democrat challenging GOP Rep. Steve King in the state's 4th Congressional District, things have changed.

Simply put, President Donald Trump happened.

"You can't deny that the country is in a fundamentally different place," Weaver said. "We have to beat Trump in 2020" and Sanders, he insisted, "feels a great responsibility to the country to make sure that, if he's getting in, that he's getting in because he is the person best positioned to do it."

Weaver has been clear on his own views. He punctuated his book on the 2016 primary and its implications with a plea for the next time around: "Run, Bernie, run." The infrastructure Sanders lacked in 2015 is in place and, should the call go out, Weaver insisted, stands ready to be activated. Minutes earlier, Pete D'Alessandro, Sanders' Iowa campaign director in 2016 - who made waves this summer when he signed on to help steer Ohio Rep. Tim Ryan around the state in 2018 - made his first cameo of the trip. He made the rounds again the next day in Fort Dodge and Ames.

"When we go into every state, there are people on the ground there who are part of what I would call 'Bernieworld,'" Weaver said. "There's already a network of people: delegates, former staffers, former supporters, new people who want to be supportive. That first meeting we went to in Indiana at the union hall, there were a number of local electeds, Democratic party officials, who might not have been there in 2015."

Also absent from the picture this time around: a prohibitive favorite like Hillary Clinton.

"The presidential stage is a lot different than running for senator or anything else. There are people who get on that stage as dark horse candidates who suddenly blossom," Weaver said, sounding genuinely curious how the 2020 crop would sort itself out, "and there are some candidates who are favorites, who get up there and suddenly wither."

Sanders' recently concluded midterms sprint began in Indiana and ended this weekend in California. In between, he headlined rallies, convened meetings with workers and seniors, and posed for untold numbers of selfies in Michigan, South Carolina, Iowa, and Wisconsin, before lighting out to Arizona and Nevada. He campaigned with Democrat Mike Levin on Friday in the Golden State's hotly contested 49th Congressional District before heading north for a rally, on Saturday, in Berkeley with Rep. Barbara Lee, a longtime ally.

Lee's seat, which she's held for two decades, is safe. But California's presidential primary, which comes early on in the 2020 primary schedule, is up for grabs.

In an interview at a homecoming parade in Ames, Iowa, Sanders coolly sniffed out and defused a question about his own future plans. (He's considering it, as he's said; this wasn't about that.) Anyway, he doesn't especially need the major media headlines, given the reach of his online operation, and probably doesn't want the kind he's most likely to generate.

"I made news today. I made big news today," Sanders said, engaging a meta analysis of his media strategy, which is anchored by a team of staffers who zip around with video equipment, entering and exiting scenes in quiet, quirky sync like characters in a Wes Anderson film. "Because I talked with four senior citizens and one senior said that the cost of her medicine soared. Extraordinary news. Because that's news that millions of people will shake their heads at."

"What you mean by news," he said, "is I gotta say something that I didn't say yesterday, but I think what's more important, and we're going to put it out on our social media, is that the cost of medicine for seniors and for everybody else is soaring, and people can't afford it."

Sanders surveyed the parking lot staging area. It was bright and cold and the band, in their cardinal and gold, were about to set off for Main Street.

"The news here," Sanders said, "is that throughout this state, people are earning starvation wages. To me that is a big story. More than anything I can tell you right now."

Sanders speaks during a rally for Nevada Democratic candidates

For decades, he has been telling it. But it was only very recently, in the course of a long and varied career, that such a wide swath of people began to really listen. On the trail in 2015 and 2016, they turned up by the tens of thousands. His critics said he never accomplished anything much during all that time in Congress, but for many, that was - in some odd sense - the point. Sanders, who arrived in Washington as Vermont's at-large representative in 1991, never bought the ticket, never took the New Democrats' ride. Now, in his late 70s, he has become a favorite of the loud, if congenitally unreliable youth vote, his visage animating armies of internet memes, his voice helping to revive a dormant passion for social democracy in American life.

Whether that means Sanders is best-positioned to win the party's nomination in 2020 is less clear.

Would he carry the same insurgent appeal this time around, particularly as so many of his potential opponents are adopting, to varying degrees, pieces of his own agenda? And even as the progressive left makes gains in minority communities, Democratic voters in 2018 have shown a unique enthusiasm for women and candidates of color. The left's biggest electoral successes, from Alexandria Ocasio-Cortez in New York to Chokwe Antar Lumumba in Mississippi, have matched that profile — a fact that only complicates these crude calculations.

At a rally with the campaign spinoff group Our Revolution in South Carolina, Sanders - as he had a night earlier to a packed auditorium of Michigan Democrats in Ann Arbor - spelled out the movement's advances and reminded supporters, as if they needed it, of the dismissive groans that greeted him in 2015.

"When I was in South Carolina and other states campaigning (before the last primary), we talked about a series of ideas, we talked about a progressive agenda and my opponent and editorial writers all over the country and the political establishment and the economic establishment, they said, 'Bernie Sanders is nuts, he is far out, his ideas are extreme. Nobody in American supports those wild ideas,'' he said, pausing a half-beat to tee up the punchline: "Well, guess what happened, folks!"

Sanders didn't wait to deliver the spoiler: "Three years have come and gone and those ideas that were seen to be radical and extreme three years ago are today mainstream, supported by the vast majority of the American people."

That the Columbia event had been panned ahead of time by some local Democratic officials, who called it unhelpful ahead of the midterms, clearly stuck in Sanders and his onstage allies' craw. South Carolina state Rep. Justin Bamberg addressed the skeptics.

"I think it's pretty clear why the Senator is here," he said. "Because the people wanted him."