SIOUX CITY, Iowa --
Sanders also regaled the crowd with the story of his long-shot 2016 presidential bid's near upset victory over Hillary Clinton in the state's presidential caucuses.
"When we came to Iowa, I think we were like at 3 percent or 5 percent in the polls. But then we had the opportunity to go all over this beautiful state ... and at the end of the day, coming from almost nowhere, we ended up tying Secretary Clinton," Sanders said.
Amid speculation that he could be mounting another presidential campaign in 2020, Sanders sharply criticized Trump as a liar who's failed to deliver on his 2016 campaign promises, including expanding access to health care for all Americans.
"I must tell you, and it gives me no pleasure to do this, that time after time, what Trump said that he would do for the American people turned out to be a lie. What he did, in many instances, was the exact opposite," Sanders said, "Donald Trump ran for president, came to Iowa, came to Vermont, and he said, ‘I, if elected, I am going to provide health care to everybody.’ But after he was elected he worked hard to try to repeal the Affordable Care Act and to throw 32 million Americans, including many people here in Iowa, off of the health care they currently have."
Scholten echoed Sanders' health care-centric message, criticizing King for his vote to repeal the Affordable Care Act.
"He voted to take away health care from thousands of Iowans and millions of Americans. And he voted to take away the protection of pre-existing conditions, and then he went to the White House to go celebrate it," Scholten said.
Voters sound off on key issues, another Sanders 2020 presidential bid
Woodbury County, where Sioux City is located, voted for Trump over Clinton by nearly 20 points in the 2016 election, but supporters of Scholten and Sanders say this year is different for the traditionally red area, and they say health care is a big reason why enthusiasm is up on the Democratic side this year.
"I think J.D.’s got a chance to knock off King. He’s run a very enthusiastic, grassroots campaign, he’s been all over the district," said Al Sturgeon, 62, an attorney and former state legislator from Sioux Falls, "I think the No. 1 issue is King’s lack of responsiveness, but second is health care, he voted to repeal and not replace and he’s never come up with a plan, so I think health care is a big issue here.”
"If I had to pick a top issue I’d say health care," said Ann Lentz, a substitute teacher from Sioux City. "The pre-existing conditions, I’m a patient with a pre-existing condition, so it strikes home for me."
"I deal with the health care system a lot because I’m a psychologist and we rely on third-party insurance payments, so that’s the way I want it to go is to have a single-payer system. I think it’s the most fair, and it’s the most efficient of all," Jim Snowden, 66, told ABC News.
When asked whether or not they'd support a Sanders 2020 presidential bid, some voters expressed hesitation at the idea.
"I don’t know if I’d support him. Bernie brings a lot of enthusiasm," Sturgeon said, "I do think the critical thing is his age. He’s got a lot of spirit, he’s the healthiest guy I’ve ever seen for his age. But by the time he would end his first term in office he’d be over 80."
"I’m not sure, it depends on who else is running," said Snowden, "I would like to see him out running, but I don’t know whether I’d wind up voting for him or not."
Others were far more eager to voice their support for another presidential run from the Vermont senator.
"I could definitely [vote for him], he’s my favorite candidate of all time just about," said Patricia Sutherland, a retired community college administrator.
"Oh yes, definitely, that’s what I’m hoping for," Lentz said.
The district is the most Republican in the state, according to statistics from the Iowa secretary of state, and despite his penchant for generating controversy, King has only failed to win 60 percent or more of the vote in his district twice during his nearly 16-year congressional career (2006 and 2012).
FiveThirtyEight rates the race as "Likely Republican," giving King a 7-in-8 chance to win re-election.
Sanders' swing began in the far western part of the state with a rally in Sioux City, with additional events planned in Fort Dodge and Ames, including a social security town hall and an appearance at the Iowa State University homecoming parade, according to Scholten's campaign.
King once again sparked outrage this week by praising a candidate for Toronto mayor, Faith Goldy, who appeared on a podcast produced by a Neo-Nazi website during last year's white nationalist rally in Charlottesville, Virginia.
Scholten condemned King's support for Goldy, writing on Twitter, "Once again, Steve King spends more time supporting far-right leaders in other countries than he does focusing on the needs of the people of our district."
The Des Moines Register, Iowa's largest newspaper, endorsed Scholten in his challenge to King last week, sharply criticizing the Republican incumbent.
"This one’s a no-brainer for any Iowan who has cringed at eight-term incumbent King’s increasing obsession with being a cultural provocateur," the Register's editorial board wrote, "In his almost 16 years in Congress, King has passed exactly one bill as primary sponsor, redesignating a post office. He won’t debate his opponent and rarely holds public town halls. Instead, he spends his time meeting with fascist leaders in Europe and retweeting neo-Nazis."
GovTrack, a site that tracks the activities of the U.S. Congress, confirms that King has indeed only been the primary sponsor of exactly one piece of legislation, H.R. 2758, which redesignated a post office in Glenwood, Iowa as the "William J. Scherle Post Office Building."
Sanders' swing sparks 2020 speculation
The trip for Sanders is part of an aggressive, nine-state campaign blitz that the Vermont Senator's team announced last week and began on Friday with a campaign rally in Bloomington, Indiana for congressional candidate Liz Watson.
"It is a diversity of Democrats on the list from some people who are unabashedly progressive to some who are progressive but not totally aligned with Bernie on every issue," Jeff Weaver, Sanders' former presidential campaign manager and current adviser, told ABC News in a phone interview last week.
Sanders also campaigned in South Carolina on Saturday, and has stops planned in Wisconsin, Arizona, Colorado, Nevada and California in the coming weeks, as speculation that he could be mounting another presidential bid in 2020 continues.
But Sanders is not the only 2020 Democratic contender visiting Iowa in the coming days.
California Sen. Kamala Harris is making her first trip to the Hawkeye State early next week, where she will rally with congressional candidate Cindy Axne in the state's 3rd Congressional Distirct and other Democratic hopefuls during her two-day swing.
Harris is set to campaign in the central and eastern parts of the state, including stops in Des Moines, Cedar Falls, Iowa City and Cedar Rapids.
“There is so much on the line this year,” Harris said in a statement released by the Iowa Democratic Party this week, "We have seen how Republicans sow the seeds of hate and division throughout our country over the last two years."
"Now it’s time to hold them accountable, at every level of government, and Iowans know that better than anyone. I’m excited to be coming to Iowa to make sure everyone uses the most powerful tool we can as Americans, our votes, to make real change in Iowa and in our country."
ABC News' MaryAlice Parks contributed to this report.