US President Donald Trump participates in a round-table discussion with business leaders at Northeast Iowa Community College on July 26, 2018 in Peosta, Iowa. Scott Olson/Getty Images

There is mounting frustration among many farmers over President Donald Trump's combative trade policies, which have significantly damaged their livelihoods and compelled some to reconsider their support of the president.

Wisconsin dairy farmer Jerry Volenec says he's no longer voting for Trump in the 2020 election, saying, "I don't think there's anything he could do at this point that could sway me to support him."

Total US farm income fell 16% in 2018, data from the Agriculture Department shows.

Wisconsin leads the nation in farm bankruptcies, according to the American Farm Bureau Federation.

The state's coveted 11 electoral votes went to Trump by 23,000 votes in 2016 — or less than one percentage point — a razor-thin margin that promises to make it another key battleground in the 2020 election.

Though farmers are some of Trump's staunchest supporters, any cracks in that constituency as a result of the trade war could prove decisive in other states like Pennsylvania and Michigan as well.

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Jerry Volenec was very drawn to the idea of a businessman that championed American farmers in the White House. So the fifth-generation dairy farmer in Montfort, Wisconsin cast a vote for President Donald Trump in the 2016 election.

In recent years, Volenec struggled with plummeting milk prices brought on by overproduction and failing export markets — and he hoped Trump's policies would help reverse the dire trend.

But Volenec's economic fortunes only worsened after Trump imposed sweeping tariffs on foreign steel and aluminum in March 2018, which set off retaliatory levies on American dairy products from China, Europe, Canada, and Mexico.

The latter two countries represented the biggest markets for Wisconsin dairy exports, and farmers like Volenec took a fierce hit. The pressure eased when they lifted the tariffs in May to prepare for the ratification of the United States-Mexico-Canada free trade agreement. The NAFTA replacement is thus far languishing in Congress.

Read more: Truckers and farmers who voted for Trump are starting to blame his policies for their economic woes

Still, Volenec had around a quarter of his annual income slashed as a result, and he characterizes the emergency federal aid received from a $28 billion program aimed at farmers hurt by Trump's trade war as "only pennies." The losses have forced Volenec to hold off buying new machinery and hiring up to three full-time workers.

"It didn't take me long to find out that my business and his business are completely different," Volenec told Insider, referring to Trump. "Even when he talks about farmers, I'm confident that his image of a farmer isn't me. His idea of a farmer is an investor that owns hundreds of thousands of acres and never gets his hands dirty."

He feels that Trump fooled him — and Volenec says he's no longer voting for him in next year's presidential election, saying, "I don't think there's anything he could do at this point that could sway me to support him."

Cracks in support among rural voters

There is mounting frustration among many farmers with Trump's combative trade policies, which have significantly damaged their livelihoods and compelled some like Volenec to reconsider their support of the president.

Total US farm income fell 16% in 2018, data from the Agriculture Department shows. And Wisconsin leads the nation in farm bankruptcies, according to the American Farm Bureau Federation.

Read more: As Trump policies deepen farmers' pain, Democrats see an opening in rural America

The state's coveted 11 electoral votes went to Trump by 23,000 votes in 2016 — or less than one percentage point — a razor-thin margin that promises to make it another key battleground in the 2020 election.

Though farmers are some of Trump's staunchest supporters, any cracks in that constituency as a result of the trade war could prove decisive in other states like Pennsylvania and Michigan as well. The three states combined swung for Trump in 2016 by only 77,000 votes.

"There's warning signs in Wisconsin everywhere President Trump turns," Milwaukee-based Democratic political strategist Joe Zepecki told Insider, pointing out Trump's "underwater approval ratings." He added: "As the trade war gets worse and the impact is felt more acutely by Wisconsin farmers, the very voters that he absolutely needs to have any shot of carrying the state again are abandoning him."

A key Trump constituency is hurting economically as a result of his trade wars

Farmers are at the core of Trump's constituency and a politically active one. A Farm Pulse survey showed the president had a 79% approval rating among them, a stark contrast to his approval numbers among the American public, which hovers between 40% and 45% in recent polling.

They are not a significant slice of the electorate. In 2012, there were 3.2 million farmers, according to the Department of Agriculture.

Over a year into trade disputes Trump started to aid manufacturers and other domestic producers he believed were assailed by global trade, sales of American soybeans, pork, wheat, and other agricultural products to China are starting to dry up. As both nations slapped tariffs on each other, total US agricultural exports to China fell to $9.1 billion last year, less than half of what it was in 2017, according to the American Farm Bureau.

A Wisconsin dairy farmer in 2017. Scott Olson/Getty Images

The administration said last week it would escalate tariffs to 30% on $250 billion worth of Chinese imports and impose another 15% tax on another $300 billion worth of goods later this year. China no longer buys American agricultural products and its raising tariffs on $75 billion of US exports.

The Trump administration has defended the short-term economic pain incurred by promising a better future for farmers. "Farmers are patriots ... and they know the long-term benefits are going to be worth it for themselves and this nation," Trump campaign communications director Tim Murtaugh recently told Reuters.

Trump also has adopted an optimistic view, tweeting in late July that under his watch, "farmers are starting to do great again, after 15 years of a downward spiral."

Matt McAlvanah, the spokesperson for Farmers for Free Trade, an advocacy group, told Insider, "We're hearing firsthand from farmers across the country not only are they struggling, but they are frustrated that the Trump administration is portraying them as doing fine."

He added: "They appreciate the president has called them patriots, but being a patriot does very little for them when they're showing up to talk to their lender and declaring bankruptcy or delinquent on their loans."

Trouble in Wisconsin, a crucial swing state

In Wisconsin, the agricultural sector powers its economy with over $100 billion annually and almost half of it comes from the dairy industry, according to the state's Department of Agriculture. And the state's three biggest trading partners are Canada, Mexico, and China.

The executive director of the Wisconsin Farmers Union, Julie Keown-Bomar, told Insider the trade wars have been "one more blow" for a dairy industry already battered by low prices.

She added: "We see in the stock market and the erratic tariff strategy that it is wreaking havoc on a poor farm economy," Keown-Bomar said. "A lot of farmers cannot afford it, they are completely in debt and they can't hold on anymore."

That was echoed by Robert Karls, the executive director of the Wisconsin Soybean Association. He disagreed with Trump's July tweet, pointing out soybean prices have dropped around 25% from $11.60 a bushel in July 2016 to $8.80 this month.

An Iowa farmer with his soybeans, Thursday, Aug. 22, 2019, at his farm in Lacona, Iowa. (AP Photo/Julie Pace) Associated Press

The US Soybean Export Council reported that shipments have also decreased 19.2 million metric tons in the first ten months of 2019 compared to the last marketing year. The lower rate of US soybean sales has fueled the demand for Brazilian soybeans in China, Bloomberg reported.

McAlvanah said economic competitors like Russia and Canada are "rapidly" filling the void and establishing new agricultural relationships with China. He added: "Its very difficult to regain markets farmers have spent decades cultivating. These relationships are built over time, they're built on trust — and when they go away overnight, they don't come back overnight."

2020 Democrats see an opportunity to make inroads with voters in rural America

The Democratic presidential candidates face an uphill battle to reclaim rural voters. In 2016, over 75% of them backed Trump over his rival Hillary Clinton, according to the Washington Post.

But the candidates aren't shying away from testing how deep voters' support for Trump runs in rural America. Some, like former Vice President Joe Biden, are directly tailoring their campaign messaging to farmers dealing with the brunt of the trade war.

Read more: Democratic presidential candidates don't want to sound too happy about the prospect of a Trump recession — even though it could be their ticket to victory in 2020

"How many farmers across this state, across this nation, have to face the prospect of losing everything, losing their farm because of these tariffs?" Biden said in Iowa last week.

But the Democratic Party's lurch to the left on immigration and other social issues threatens to limit their appeal. And most political analysts don't believe farmers will decisively turn against Trump next year.

"Most farmers in the rural parts of the U.S. have conservative values" that more closely matches with the GOP, Republican political strategist Ray Zaborney told CNBC. "Between their values and the president standing up for them, they're willing to give him some leeway" on Trump's trade wars.

While alleviating the impact of the tariffs is an important message for candidates to strike, Zepecki says he believes the 2020 Democrats can make inroads with rural voters by focusing on access to affordable healthcare, calling it "a winning strategy."

Volenec is a voter who previously backed President Barack Obama in 2012. And he says he's biding his time before choosing who to vote for in the wide Democratic primary field.

"I'm just kind of taking a step back and watching right now," Volenec says.

But a candidate who has drawn his interest? Sen. Bernie Sanders, who handily carried the state in its 2016 Democratic primary.