The trucking industry was a key source of support for Donald Trump in the 2016 election.

Executives from the $800 billion industry have met with the president several times to help him push his healthcare and tax initiatives.

Still, leaked audio of a 2018 dinner published by The New York Times over the weekend showed that Trump's knowledge of the trucking industry has surprising gaps.

Trump did not know that trucks run on diesel. He also did not appear to be aware of two critical issues roiling the trucking industry: the truck-driver shortage and the implementation of electronic logging devices.

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A leaked audio recording of a 2018 dinner with President Donald Trump and key donors has provided new insight into the president's dealings with Ukraine, as well as his relationship with the businessmen Lev Parnas and Igor Fruman, two crucial characters in Trump's impeachment scandal.

The recording of the dinner on April 30, 2018, revealed something else: The president's knowledge of trucking is less than comprehensive.

For a little more than 10 minutes of the 83-minute audio clip, Trump talked with the major donors attending the dinner about the $800 billion trucking industry.

The New York Times identified one executive as Barry Zekelman, the billionaire who owns North America's largest maker of steel tubes.

Another attendee, according to The Times, was Wayne Hoovestol, who owns several trucking companies in the Midwest, including Eagle Express Lines. According to Transport Topics, Eagle Express had revenue of more than $450 million in 2018 and was the second-largest carrier of US Postal Service mail.

Two 18-wheeler trucks on the South Lawn of the White House. AP Photo/Andrew Harnik

On the day of the dinner, a limited-liability company called DRT donated $250,000 to America First Action, a pro-Trump super PAC. DRT shares the same address as a truck-leasing company that Hoovestol owns, OpenSecrets reported. Several months later, DRT donated $10,000 to a super PAC associated with Senate Majority Mitch McConnell.

From 2002 to early 2019, Hoovestol and his wife donated nearly $120,000 to various Republican candidates, OpenSecrets said.

Read more: A recession slammed trucking last year — and experts predict that 2020 will bring more bankruptcies and plunging truck orders

Hoovestol did not immediately respond to Business Insider's request for comment. A media representative from the American Trucking Association told Business Insider that he was not aware of whether any members of the organization attended the dinner.

The White House did not immediately respond to a request for comment.

'Why can't you? Just not as strong?'

In the recording, after a short conversation about Tesla and electric passenger trucks, someone identifying themselves as a trucking executive who had worked with the USPS begins talking about the challenges with fueling semitrucks. Here's the conversation that followed:

Trump: What do you mean trucks? What do you do? Where did you say you work at?

Trucking executive: Our main thing we do, we haul mail for the Postal Service.

Trump: Oh I see. So you know the difference, right? You have every kind. Is there anything like gasoline?

Trucking executive: Nope. Well, diesel is trucking.

Trump: How is diesel compared to regular gasoline?

Trucking executive: Well, diesel in a semi — you can't run gasoline in a semi.

Unidentified voice: Right, big tractors.

Trump: Why can't you? Just not as strong?

Trucking executive: It doesn't have the BTUs that diesel has.

Other people then talked with Trump about other major issues in the industry, including the truck-driver shortage and the implementation of electronic logging devices.

Trump also appeared unaware that truck drivers have safety regulations that prevent them from driving more than 11 hours a day.

More than 4,670 people died in accidents involving large trucks in 2018, including 885 truck occupants, the National Highway Traffic Safety Administration said.

"You mean they can only drive so much?" Trump said in the recording. "Like a pilot? I didn't know that."

Truckers and their employees have supported Trump and met with him multiple times

Trucking executives and industry experts who listened to the tape told Business Insider they were astonished by Trump's ignorance.

They said they were doubtful that the president would not have been told about many of the basic points covered in the 10-minute conversation. The gaps in Trump's knowledge — including his ignorance that 18-wheelers run on diesel, not gasoline — contrast with his interactions with the trucking industry.

The April 2018 dinner at the Trump International Hotel in Washington was not the first or last time Trump has interacted with the trucking industry.

A year earlier, Trump welcomed truck drivers and ATA representatives to the White House to discuss healthcare. Trump even climbed in a big rig parked on the South Lawn and tooted the horn as transportation executives who had gathered around the truck laughed.

Trump in the truck. Carlos Barria/Reuters

Several weeks before the dinner, ATA representatives returned to the White House to champion Trump's 2018 corporate tax cuts.

"Our industry could not ask for better representatives than these to talk about the benefits of the president's tax reform package," said Chris Spear, the ATA's president and CEO.

Read more: Truckers voted for Trump in droves. Now they say his trade war is 'killing' their ability to make a living.

America's truck drivers — of which there are 1.8 million — were a key source of support for Trump in 2016, a July 2016 Overdrive magazine survey suggested.

The industry has lent significant monetary support too. The trucking industry contributed just over $9 million in the 2016 election, 81% of which went to Republican candidates; Trump's 2016 campaign received $331,000 of that, according to Federal Election Commission documents published by OpenSecrets.

Email the reporter at rpremack@businessinsider.com.