(CNN) —  

Ohio Sen. Sherrod Brown wasn’t aiming for the biggest crowd on the opening stop of his four-state tour to explore a presidential run – and on a frigid night, he didn’t get one.

He was drawn to this northern Iowa town by a different set of numbers: President Donald Trump won this county with 57% of the vote in 2016. Four years earlier, Barack Obama carried it by 60%.

That dramatic shift – a pattern repeated over and over across the industrial Midwest and the Great Lakes, from Iowa to Pennsylvania – is one of the most vexing challenges facing Democrats in 2020. And it’s the central argument for Brown as he considers whether to join the party’s growing field of presidential candidates.

“Democrats learned a lot of lessons, but the most important lesson is we write off no place in the country,” Brown said in an interview here. “I’m weary of Democrats that say you only talk to progressives to win and excite the base.”

He is testing a potential presidential candidacy through what he’s calling the “Dignity of Work” tour. One handshake at a time, he’s presenting himself as a true populist to voters in visits to Iowa, New Hampshire, Nevada and South Carolina, all of which open the Democratic nominating season a year from now.

Along the way, Brown is touting his Ohio roots and his re-election to a third term in the Senate. It was a stand out Democratic victory in an increasingly red state, which Trump won by eight points in 2016.

“An outspoken progressive can win – and win decisively – in the heartland,” Brown said, an example of why he believes Democrats should not ignore Trump country and how his race last fall could be a model for the party.

He is one of at least nine senators ambitiously eyeing a bid for the Democratic nomination. He tells voters he hasn’t spent a lifetime thinking of being president like many of his colleagues, even dusting off this self-effacing line he’s used over the years: “The only cure for the presidential virus in the US Senate is embalming fluid.”

After shaking hands with a few dozen Democratic activists who braved sub-zero conditions here Thursday night to see him, Brown made clear the party’s field of presidential hopefuls is missing an argument for why blue-collar workers should vote Democratic.

“I think that voice needs to be stronger,” Brown said.

It’s a tepid, yet unmistakable critique as the Democratic lineup takes shape.

After his fellow senator, Cory Booker of New Jersey, jumped into the race on Friday, Brown was asked by reporters about his potential rivals. He could have delivered a standard response, as most Democrats do, singing the praises of his colleagues.

Instead, Brown said this: “I like all of my colleagues that are running. I like some more than others. I’ll leave it at that.”

He quickly added: “But I like Cory and more power to him. He’s been looking at this for a while. He’s my friend.”

But Brown does not mince words as he pointedly makes the case that Democrats must carefully choose a nominee to confront the President. He doesn’t back away from a progressive agenda – in many ways, the party has moved leftward toward Brown – but he said it must be presented with a non-condescending message for rural and working-class voters.

Asked whether he believes Democrats should nominate a candidate from the middle of the country, rather than the East or West coast, he replied: “Our party needs to nominate somebody who can win the industrial Midwest, the heartland, the Great Lakes states, the plains states from Pennsylvania to Iowa. We’ll see how the voters decide that.”

Mary Weaver, who sat beside Brown on Friday afternoon during a roundtable discussion at the library in the town of Perry, is one of those voters. She told him she would meet every candidate who comes within a 50-mile radius of her home in central Iowa.

“I want a candidate that brings me hope and brings me ideas that can beat Donald Trump,” Weaver said, looking him squarely in the eye.

“In that order?” Brown said.

“I think we need hope first,” she responded.

On his listening tour, Brown did just that – listened to concerns, without offering many ideas, solutions or hope. As he left the room, Weaver said she enjoyed meeting Brown and had a positive impression, but quickly added that he had not won her over: “We need to meet them all.”

For two years, Democrats have been united in their overwhelming opposition to Trump. But the divisions inside the party – over policy and even personality preferences – are bubbling just below the surface.

Brown met with several farmers, including Weaver, her husband and son, at the gathering in Perry. The meeting offered an early window into the obstacle course Brown likely faces on trade. He was among the staunchest critics of NAFTA, which largely benefited Iowa farmers who are now caught in the middle of a costly trade war with China.

“Full disclosure. I supported the tariffs originally,” Brown said Friday, noting that he and Trump share some views on trade. “They are a temporarily tool to get to a certain point – not a long-term trade policy. Trump has made them a long-term trade policy.”

If he runs for president, this topic will be explored in far more depth than Brown made time for on Friday afternoon

“This clearly wasn’t enough time to get into anything very deeply,” said Warren Varley, a lawyer and farmer who sat across the table from Brown and noted that he had a positive initial impression, but far more questions.

As the senator made his way to the door, making small talk on the way out of the library’s meeting room, Varley said he is still sizing up the large Democratic field.

“You need a scorecard to keep up,” he said. “I share Senator Brown’s concern that we not go off the rails trying to please progressives. It’s important to keep progressives enthused, but we need to have a big tent too.”

“I’m more inclined to support a more moderate candidate like Amy Klobuchar,” Varley added, raising the name of the Minnesota senator without prompting. “I’d sure like to see her run.”

And Klobuchar is strongly considering it, several confidants say, a move that would add not only another senator to the mix, but another formidable candidate who believes Democrats should not cede Trump country.