Truck drivers tend to be conservative.

But a growing group of them are moving away from President Donald Trump.

They say his trade wars and a slew of tax changes have ruined their ability to make a living.

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Morris Coffman has been a truck driver for 35 years. And he's been a conservative for even longer than that — his whole life.

"That said," Coffman told Business Insider, "[Trump] is absolutely a moron. His idiotic ideas will tank the economy even further."

Truckers, like Coffman, lean conservative. A Verdant Labs analysis of Federal Elections Commission data found that nearly three-quarters of truck drivers are Republican — one of the most conservative jobs in America, along with surgeons and farmers.

And truck drivers supported Trump in droves, according to an Overdrive magazine survey from 2016. About 75% said they planned to vote for Trump, up from 66% who supported Sen. Mitt Romney, the Republican presidential nominee in 2012.

But a sharp downturn in the trucking industry and a slew of tax changes have hampered their ability to make a living. And many connect those two trends to Trump's economic policies.

"He has not affected our business in a positive way," said one truck driver who asked to be quoted anonymously for fear their small business might suffer. "He's killing our business. If consumers aren't buying, then there is no demand. This really isn't about my political leanings — it's pure business."

Trump's tax reworking in 2017 led to many truck drivers having to pay hundreds in taxes this year, thanks to a change in per-diem laws. Dennis Bridges, an accountant who specializes in doing taxes for truckers, told Mother Jones in April that 75% of his clients saw an unusually large tax payment, and about 20% had to fork over more than $5,000.

That might've been bearable in 2018, when trucking capacity was tight, the industry was raking in cash, and truckers saw their pay jump. But now the trucking "bloodbath," as Coffman and other truckers describe current transportation conditions, has meant low rates and low pay for truckers. Trucking has been in a recession since late 2018.

Read more: 2,500 truck drivers have lost their jobs in 2019 as the transportation 'bloodbath' rolls on. Here's the full list of bankrupt trucking companies.

Transport research groups reported that the volume of trucks purchased in July fell to its lowest level in nearly 10 years. The number of loads needing to be moved in the spot market tumbled by 37% this July compared to one year ago, and rates have fallen by as much as 18%.

"I have witnessed many ups and downs in the industry but nothing like this," Coffman told Business Insider. "Many, many owner-operators and drivers have either lost equipment or lost a job in the last year."

The Cass Freight Index says year-over-year trucking volumes have slipped for eight consecutive months. In June, factory-activity growth was its slowest since October 2016, according to the Institute for Supply Management. That means manufacturers didn't receive as many orders and there were fewer things to move.

Truckers say the dip in manufacturing numbers — which they say are tied to Trump's trade war — is one reason there are so few jobs.

"The truth about the rates being so low is Trump's trade policies," JL Sims, a truck driver, told Business Insider. "Manufacturers are scared. Last month's manufacturing jobs numbers finally began to reflect the reduced production. Everyone looks at the unemployment rate and thinks, mistakenly, that the economy is in great shape. Manufacturing tells the real story."

Read more: Truckers can't pay off their fuel cards, and it's a 'sure sign' more trucking bankruptcies are coming

Analysts in trucking are hesitant to make the same sort of connections, however.

DAT Solutions senior analysts Mark Montague and Peggy Dorf previously told Business Insider that the downturn in global trade has affected only certain regions of the US trucking industry.

Experts have said an exceptionally vibrant 2018 may be the bigger reasons for the downturn in trucking. Last year, trucking was incredibly profitable, with record-low bankruptcies, remarkably high rates, eight-month-long wait lists for new trucks, and huge bumps in trucker pay.

"I view it as the market correcting itself," Cowen's Jason Seidl previously told Business Insider. "We basically put too much capacity out there in the marketplace, and you saw that by the rates dropping very hard. The market can only take so much of that, so it corrects itself. And this is the market just correcting itself."

Whatever the cause of the downturn, truckers are a key demographic for any politician to target. The segment of truckers called owner-operators, for instance — who are independent, rather than company drivers — are fiercely engaged with politics on the national level.

Nearly 90% are registered voters, according to the Owner-Operator Independent Drivers Association, compared to about 78% of the general population. More than half have contacted an elected official.

Trump has previously catered to truckers, pledging to slash taxes to help their businesses. "America first means putting American truckers first," he said at a 2017 trucker event.

But truckers, including conservative ones, don't believe Trump has lived up to his promise.

"You can not bully your way to a good economy," Coffman said.