That included Des Moines, where close to 800 people streamed to a university auditorium on Friday night, and Waterloo, where more than 500 people gathered in a theater on Sunday afternoon.
The Vermont senator had the support of 16 percent of likely Democratic caucusgoers in a Des Moines Register/Bloomberg News Iowa poll earlier this month, to Clinton's 57 percent.
So who's coming to hear him speak?
This weekend, there were those fully sold on the self-described democratic socialist -- they were the ones wearing “Bernie for president” t-shirts and holding the “Feel the Bern” signs. There were some others shopping for an alternative to Clinton, the formidable front-runner. Still others were merely curious about the fuss surrounding the frumpy politician who’s seen his poll numbers surge.
Terry Pensel, a Web developer who traveled more than 90 minutes from Guttenberg to see Sanders in Waterloo, was among those in the fully-sold category.
“I don’t want to bash Hillary Clinton or any of the other Democrats, but I don’t see them having a plan to deal with the concentrated wealth,” said Pensel, 47, as he left the auditorium with several yard signs and bumper stickers tucked under his arm. “They’re giving lip service to a lot of the issues Bernie has been talking about for a long, long time.”
Those issues, as Sanders described them, include the the “grotesque level of wealth and income inequality” in the country, the corrosive effects of big money on politics and the “disastrous” trade deals the country has entered into.
While Pensel was clearly pumped up about Sanders’s prospects, he also complained that the media -- the corporate-controlled media, as he described it -- has given Clinton so much more attention than Sanders.
Tara Monson, meanwhile, was fired up about Sanders even before he appeared at a union hall in Marshalltown on Saturday.
The 31-year-old mother of two arrived with her 6-month-old daughter in a carrier on her chest. The carrier sported a Bernie button, and Munson’s daughter was wearing a bow and a homemade “Feel the Bern” t-shirt.
“I never really heard of Bernie Sanders until he started running, and he’s really grabbed me,” said Monson, who performs audits for a goat farm. “He brings a different ball to the game.”
Monson said she particularly liked what Sanders has been saying about policies affecting families. He is calling for guaranteed vacation, family leave and sick time and says Americans should be working fewer hours. One of the biggest laughs Sanders gets on the trail comes from rattling off how many more hours a year Americans work than the French.
“My husband has been trying to get me to move to a socialist country for years,” said Monson, whose spouse hails from Norway. “Now I’m telling him it might come here.”
On a more serious note, she said that she’s not a big Clinton fan and thinks “it’s a little ridiculous that the Democratic party is just letting her have the spotlight.”
For every fan like Pensel and Monson who attended Sanders events, though, it seemed there was also someone like Ed Canade, who said he likes what the senator has to say but has some reservations about making him the party’s nominee.
Canade, a 68-year-old semi-retired paramedic, said he considers Clinton “a polarizing candidate” and is looking for an alternative. But he wasn’t ready to commit to Sanders after seeing him in Marshalltown.
“He kind of speaks with a grumpy-old-man kind of tone,” Canade said of Sanders, who is 73. “I don’t know if people are going to find that appealing.”
Canade said Sanders also doesn’t look the part of a president, adding: “I know glamor and appearance are a thing in politics.”
Canade said he is considering another Democratic candidate, former Maryland governor Martin O’Malley. But, he said, “I’m concerned that he’s this unknown at this point in the race.”
Kathleen Murrin, who came to see Sanders Friday night in Des Moines, said she can envision Sanders as the Democratic nominee, dismissing talk by pundits that Sanders would have a hard time winning a general election.
“Have you looked at the Republicans who’ve come into this state?” asked Murrin, 68, who works for a nonprofit organization focused on mental health issues.
Sanders, Murrin said, has “got real solutions that he’s talking about. And he’s got real heart.”
Still, she said she’s not ready to commit. For her, it’s partly a sense of duty.
“I’m an Iowan,” Murrin said, pledging to check out other candidates as well. “We have a long way to go to the caucuses.”
She said she has her doubts about Hillary -- “she’s very polarizing and tried this before” -- and said she just doesn’t know that much about O’Malley or the other Democrats.
Lance Wilson, who caught Sanders on Saturday night at a labor dinner in Cedar Rapids, said he admires Sanders for running at a time when Clinton’s presence kept many other Democrats out of the presidential race.
“Because Hillary is so big, other candidates don’t want to step out,” Wilson said. “What I like about Bernie is he’s willing to step out.”
Wilson, 36, works in collections for a company that makes car loans. Many of the people he talks to are down on their luck, he said, and what Sanders is saying should resonate with them. Wilson also thinks Clinton is too much of a centrist and likes Sanders’s candor.
“He says what needs to be said rather than what people want to hear,” Wilson said.
Dan Friedrichs, co-chairman of the Boone County Democrats, made a similar point in the Marshalltown union hall, where he came to see Sanders on Saturday.
“What people like is he shoots from the hip, but he has something substantive to say,” Friedrichs said. “He’s talking the language the middle class wants to hear: Protect us. That’s what Bernie is all about.”
A retired teacher, Friedrichs said he particularly likes Sanders call for free public university tuition and universal pre-kindergarten. But for now, Friedrichs said, he’s encouraging people to see all the Democratic candidates before making a final decision.
Bob Handel, a semi-retired real estate agent, is among those who don’t need any more convincing. A self-described “Sanders groupie,” Handel traveled from Davenport to Cedar Rapids on Saturday to catch yet another appearance by the Vermont senator.
Handel said that the race should be about issues, and that there’s too much about Clinton that detracts from that -- the email controversy, countless articles about the Clinton Foundation’s donors and the Benghazi controversy.
Sanders, meanwhile, has a message that should resonate broadly, Handel argued.
“If people get past the socialism and just hear him, these aren’t far-out, crazy ideas,” he said. “I think people are going to get behind him.”